WO2024026576A1 - Composition and process for cast molding objects with titanium carbide coating - Google Patents

Abstract

OF THE DISCLOSURE A composition for cast molding comprises 20-70 wt% Ti powder of 200-300 mesh, 3-20 wt% graphite powder of 200-300 mesh, 3-30 wt% tungsten carbide or titanium carbide powder of 140-325 mesh, and 3-70 wt% metal powder of 100-200 mesh. During a process of cast molding, a precursor comprising the composition is attached to an internal surface of a mold and a cast liquid is casted in the mold to form a cast object and cause the precursor to form a coating comprising titanium carbide (TiC) on the object. The cast object so produced may comprise chromium and iron or steel, and have a surface coated by the TiC coating and an uncoated surface. The uncoated surface has 35-65 HRC hardness and the coated surface has a higher hardness by 3-8 HRC.

Description

COMPOSITION AND PROCESS FOR CAST MOLDING

OBJECTS WITH TITANIUM CARBIDE COATING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit and priority of Chinese Invention Patent Application No. 202210939035.6, filed 5 August 2022, the entire contents of which are incorporated herein by reference.

FIELD

[0002] The present disclosure relates generally to cast molding of iron or steel objects, and specifically to compositions and processes for forming titanium carbide coating on cast objects during cast molding.

BACKGROUND

[0003] Erosion and wear resistant chromium cast iron is useful in many industrial applications. Chrome cast iron known as chrome white iron or white cast iron (or simply “white iron”) includes martensite and a relative low content of chromium. Steel alloys may include martensitic steel and contain iron, chromium, and carbon. High- chromium cast iron is more wear-resistant than many metal alloys and white cast iron and is considered by many as one of the best wear-resistant materials in industrial applications.

[0004] Objects made of ferrous alloys may be formed by casting or cast molding in the desired shapes and dimensions. The surfaces of cast objects can be reinforced with titanium carbide (TiC) to improve the surface properties such as increased resistance to wear and impact stress. For example, hierarchical composite materials have been used to coat cast objects of ferrous alloys with TiC coating to further improve resistance to wear and impact stress. For some industrial applications, only one or more selected surface portions of the cast objects need to be coated with a TiC coating for localized hardening, reinforcement, or strengthening. Selectively applying localized TiC coating can reduce costs and conserve energies and materials. [0005] It is thus desirable to provide improved materials and processes for cast molding objects with localized TiC coating.

SUMMARY

[0006] In a first aspect of the present disclosure, there is provided a composition for forming a titanium carbide coating on a surface of a cast object during cast molding. The composition comprises: (i) 20 wt% to 70 wt% of titanium (Ti) powder of 200 mesh to 300 mesh, (ii) 3 wt% to 20 wt% of graphite powder of 200 mesh to 300 mesh, (iii) 3 wt% to 30 wt% of carbide powder of 140 mesh to 325 mesh, and (iv) 3 wt% to 70 wt% of metal powder of 100 mesh to 200 mesh. The carbide powder comprises tungsten carbide or titanium carbide.

[0007] In selected embodiments, the above composition may comprise 30 wt% to 60 wt% of Ti powder of about 300 mesh, 5 wt% to 15 wt% of graphite powder of about 300 mesh, 10 wt% to 25 wt% tungsten carbide of about 325 mesh, and 15 wt% to 50 wt% of metal powder of 100 to 200 mesh.

[0008] In some embodiments, the metal powder may consist of 0 wt% to 60 wt% of Ni, 0 wt% to 10 wt% of Mo, 0 wt% to 10 wt% of Cu, 0 wt% to 60 wt% of Co, 0 wt% to 10 wt% of Si, 0 wt% to 10 wt% of a rare earth, 0 wt% to 5 wt% of Mg, 0 wt% to 5 wt% of B, and Fe (the Fe being the balance making up to 100 wt%). In other embodiments, the metal powder may consist of 0 wt% to 60 wt% of Ni, 3 wt% to 10 wt% of Mo, 5 wt% to 10 wt% of Cu, 2 wt% to 60 wt% of Co, 1 wt% to 3 wt% of Si, 1 wt% to 3 wt% of a rare earth, 1 wt% to 5 wt% of Mg, 1 wt% to 3 wt% of B, and Fe (the Fe being the balance making up to 100 wt%).

[0009] In another aspect of the disclosure, there is provided a method of cast molding to form a cast object comprising a titanium carbide coating on a surface of the cast object. The method comprises attaching a precursor material comprising a composition disclosed herein to an internal surface of a mold; casting a cast liquid in the mold to form the cast object, wherein the casting also causes the precursor material attached to the internal surface of the mold to form a coating comprising titanium carbide (TiC) on a corresponding surface of the cast object adjacent to the internal surface of the mold. [0010] In selected embodiments, one or more of the following options may be selected in the above method. The composition may be mixed in a ball mill for 1 to 24 hours to form the precursor material. The attaching may comprise forming a paste comprising the precursor material, a binder, and water; and covering the internal surface of the mold with the paste. The internal surface of the mold may be covered by a layer of the paste having a thickness of 1 mm to 30 mm, such as 3 mm to 20 mm. The binder in the paste may be 0.5 wt% to 3 wt% of the precursor material, and the water in the paste may be 30 wt% to 40 wt% of the precursor material. The binder may comprise a polyvinyl alcohol of 0.5 wt% to 3wt% of the precursor material. The attaching may alternatively comprise forming coating blocks comprising the precursor material and a lubricant; and affixing the coating blocks to the internal surface of the mold. The lubricant in the coating blocks may be 3 wt% to 8 wt% of the precursor material. Affixing the coating block may comprise securing the coating blocks in position with dowel pins. The precursor material and the lubricant may be mixed and compressed under a pressure of at least 15,000 kg/cm² to form the coating blocks. The lubricant may be a stearic acid or paraffin wax. The coating blocks may comprise 3 wt% to 8 wt% of the lubricant and having a thickness of 2 mm to 100 mm, such as 2 mm to 40 mm. An antistick layer may be formed on a selected portion of the internal surface of the mold. The antistick layer may comprise an alcohol-based paint. The precursor material may be attached to one or more selected portions of the internal surface of the mold. The cast liquid may comprise (i) iron and chromium or (ii) a steel alloy. The mold may comprise a shell mold precoated with molding sand. The cast object may be further treated to harden the cast object.

[0011] In a further aspect, a cast object is produced according to a method disclosed herein, and comprises a body comprising (i) chromium and (ii) iron or steel. The body has a coated surface coated by the coating comprising TiC and an uncoated surface. The uncoated surface has a first hardness of 35 to 65 HRC and the coated surface has a second hardness being 3 to 8 HRC higher than the first hardness.

[0012] Other aspects, features, and embodiments of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the figures, which illustrate, by way of example only, embodiments of the present disclosure:

[0014] FIG. 1 is a schematic diagram illustrating a process for cast molding a cast object, in accordance with an embodiment of the present disclosure;

[0015] FIG. 2 is a block diagram illustrating a cast molding process, in accordance with an embodiment of the present disclosure;

[0016] FIG. 3 is a top view of a cast pump cover;

[0017] FIG. 3A is a side cross-sectional view of the pump cover taken along line 3A-3A in FIG. 3;

[0018] FIG. 3B is another cross-sectional view of the pump cover taken along the line 3B-3b in FIG. 3;

[0019] FIG. 4A is a cross-sectional view of a cast pipe elbow;

[0020] FIG. 4B is an axial cross-sectional view of the cast pipe elbow of FIG. 4A along line 4B-4B;

[0021] FIG. 5A is a front cross-sectional view of a cast plate;

[0022] FIG. 5B is top view of the cast plate of FIG. 5A;

[0023] FIG. 6 is a schematic cross-sectional view of a cast rod tooth;

[0024] FIG. 7A is a schematic top view of a front guard plate;

[0025] FIG. 7B is a cross-sectional view of the front guard plate of FIG. 7A, taken along line A-A;

[0026] FIG. 8A is a schematic top view of another front guard plate;

[0027] FIG. 8B is a cross-sectional view of the front guard plate of FIG. 8A, taken along line B-B;

[0028] FIG. 9A is a schematic top view of another front guard plate;

[0029] FIG. 9B is a cross-sectional view of the front guard plate of FIG. 9A, taken along line C-C;

[0030] FIG. 10A is a schematic top view of another front guard plate;

[0031] FIG. 10B is a cross-sectional view of the front guard plate of FIG. 10A, taken along line D-D;

[0032] FIG. 11 A is a schematic cross-sectional view of a rear guard plate;

[0033] FIG. 11 B is a top view of the rear guard plate of FIG. 11 A;

[0034] FIG. 12A is a schematic cross-sectional view of another rear guard plate;

[0035] FIG. 12B is a top view of the rear guard plate of FIG. 12A;

[0036] FIG. 13A is a schematic cross-sectional view of a cast plate;

[0037] FIG. 13B is a top view of the cast plate of FIG. 13A;

[0038] FIG. 14A is a schematic cross-sectional view of another cast plate;

[0039] FIG. 14B is a top view of the cast plate of FIG. 14A;

[0040] FIG. 15 is a top view of another cast plate;

[0041] FIG. 16A is a schematic front view of a cast shovel tooth;

[0042] FIG. 16B is a top view of the cast shovel tooth of FIG. 16A;

[0043] FIG. 17A is a schematic front view of a cast bucket tooth; and

[0044] FIG. 17B is a top view of the cast bucket tooth of FIG. 17A.

DETAILED DESCRIPTION

[0045] Example embodiments disclosed herein relate to processes for cast molding cast objects and coating compositions for coating the cast objects during the cast molding process.

[0046] In an embodiment, a composition for forming a titanium carbide (TiC) coating includes a mixture of powder materials. The mixture includes 20 wt% to 70 wt% of titanium (Ti), 3 wt% to 20 wt% of graphite (C), 3 wt% to 30 wt% of carbide, and 3 wt% to 70 wt% of metals, all in powder forms. The carbide powder may include powders of tungsten carbide, titanium carbide, or a combination thereof.

[0047] The powders may have different particle sizes, such as from 100 to 350 mesh depending on the specific materials used and the processing requirements in a particular application. In some embodiments, the Ti and graphite powders may be 200 mesh to 300 mesh, such as about 300 mesh. The carbide powder may be 140 mesh to 325 mesh, such as about 325 mesh. The metal powders may be 100 mesh to 200 mesh.

[0048] In some embodiments, the mixture may comprise 30 wt% to 60 wt% of Ti, 5 wt% to 15 wt% of graphite, 10 wt% to 25 wt% tungsten carbide, and 15 wt% to 50 wt% of the metal powder.

[0049] In some embodiments, the mixture may comprise 30 wt% to 60 wt% of Ti powder of about 300 mesh, 5 wt% to 15 wt% of graphite powder of about 300 mesh, 10 wt% to 25 wt% tungsten carbide of about 325 mesh, and 15 wt% to 50 wt% of metal powder of 100 to 200 mesh.

[0050] In some embodiments, the metal powder may consist of 0 wt% to 60 wt% of Ni, 0 wt% to 10 wt% of Mo, 0 wt% to 10 wt% of Cu, 0 wt% to 60 wt% of Co, 0 wt% to 10 wt% of Si, 0 wt% to 10 wt% of a rare earth, 0 wt% to 5 wt% of Mg, 0 wt% to 5 wt% of B, and Fe. For clarification, the iron content in the mixture is adjusted based on the actual weight percentages of the other listed components so the balance is Fe, which makes up to 100 wt%.

[0051] In some embodiments, the metal powder may consist of 0 wt% to 60 wt% of Ni, 3 wt% to 10 wt% of Mo, 5 wt% to 10 wt% of Cu, 2 wt% to 60 wt% of Co, 1 wt% to 3 wt% of Si, 1 wt% to 3 wt% of a rare earth, 1 wt% to 5 wt% of Mg, 1 wt% to 3 wt% of B, and Fe. [0052] To form coatings on ferrous metal objects such as high-chromium cast iron objects, the coating materials should be carefully selected to accommodate or in view of the specific properties of ferrous metals, which are different from those of non-ferrous metal copper alloys. For example, non-ferrous metal copper alloys have relatively high ductility and fatigue resistance. By comparison, high-chromium cast iron has a relatively low cast toughness and is a brittle wear-resistant material. Therefore, the selection of the components in the coating composition should take into account of these and other characteristics and properties of high-chromium cast iron. For instance, it may be desirable that the ingredients in the coating composition will not negatively affect or degrade desired characteristics or properties of the high- chromium cast iron. As an example, including a boron-based ceramic material in the coating composition may introduce an excessive boron content into the surface of the cast object, which may reduce the toughness of the bonded layers in the cast object, and increase the cracking instability. Including excessive aluminum in the coating composition may increase the risk of forming hydrogen pores in the cast object. As the solubility of borax is low, inclusion of borax in the coating composition may introduce slags or particulate residues onto the cast object.

[0053] The powder mixture may be prepared by mixing the selected materials in selected proportions, such as in a ball mill. For example, the selected metal powders in the desired proportions may be mixed and grinded in a ball mill for about 1 hour to about 24 hours to form a metal powder mixture having an average particle size of 100 to 200 mesh. The metal powder mixture, Ti powder, graphite powder, and carbide powder in the selected proportions may then be mixed in the ball mill for about 1 hour to about 24 hours until the powders are thoroughly and uniformly mixed to form an initial coating mixture.

[0054] The powder mixture may be premixed and stored, or may be mixed prior to use on site. The premixed materials or the initial coating mixture may be transported to a production site and then further treated as described below.

[0055] The initial coating mixture may be further treated to form a paste before use. For example, a binder and water may be added to the initial mixture and stirred or agitated to form a paste, as will be further described below. The binder may be a polyvinyl alcohol, or any other suitable binder depending on the materials in the initial mixture. The binder content in the resulting paste may be 0.5 wt% to 3 wt% of the powder materials of the initial mixture in the paste. The water in the paste may be 30 wt% to 40 wt% of the powder materials of the initial mixture in the paste.

[0056] Alternatively, the initial mixture may be further treated to compact the powder materials and a lubricant into compacted blocks, to be used as coating blocks. The lubricant in the coating blocks may be 3 wt% to 8 wt% of the powder materials. The powder materials and the lubricant may be mixed and compressed under a compacting pressure of 15 ton/cm² or higher to form the coating blocks. The lubricant may be a stearic acid or a paraffin wax. The coating blocks may have a thickness of 2 mm to 100 mm, such as 2 mm to 40 mm. The coating blocks may have standard sizes and shapes for use in casting molding processes.

[0057] The cast objects may be formed using any suitable casting techniques. For example, the cast objects may be formed by coated sand shell casting, precoated resin sand shell casting, steel shell mold casting, other sand shell mould casting, coated sand core casting, or the like.

[0058] In an embodiment, a process S100 for casting molding uses the coating mixture, particularly the coating paste, to form localized TiC coatings as illustrated in FIG. 1.

[0059] At stage S101 , a binder 102, a powder mixture 104 as described above, and water 106 are mixed in a mixing vessel 108 to form a coating paste 110. The binder 102 may be an aqueous solution containing 1.2 wt% polyvinyl alcohol. The weight ratio of the powder mixture (on a dry basis) to the binder and to water in the vessel 100 or the final coating paste 110 may be 1 :(0.005-0.03) and 1 :(0.3-0.4) respectively [or 1 :(0.005-0.03):(0.3-0.4)], such as 1 :(0.01-0.02):(0.3-0.4) or 1 :(0.01-0.012):(0.3-0.4).

[0060] At stage S120, a layer 128 of the coating paste 110 is applied to a selected portion 126 of an internal surface 122 of a casting mold 124 to cover the selected surface portion 126.

[0061] As illustrated in FIG. 1 , the mold 124 may include two or more mold parts, such as a lower part and an upper part. The paste layers may be formed on one or more of the mold parts. Mold 124 may be a sand mold, and have sand coated or treated internal surfaces. The mold 124 may be a shell mold pre-coated with molding sand.

[0062] The thickness of the paste layer 128 may be adjusted based on the particular application. In some embodiments, the layer thickness may be about 1 mm to about 30 mm, such as 3 mm to 20 mm.

[0063] The coating paste may be prepared so that it has a suitable viscosity, which may be a moderate viscosity, so that the resulting paste is suitable for forming a coating layer and adhering to the mold’s internal surface, which may be a sand- coated surface. The amount of water in the paste may be adjusted based on the desired thickness of the paste layer. For example, for a thinner paste layer, the paste material may be less viscous and has a higher water content; and vice versa. In turn, the thickness of a paste layer may be selected based on the required coated surface properties.

[0064] To clearly align the edges of the paste layer and to temporarily hold the applied wet paste in place, frames, such as wood frames or metal frames, may be used. The frames may be mounted on the mold surfaces around the areas to which the coating paste is to be applied. The height of the frames may be adjusted based on the desired thickness of the paste layer. With the frames mounted in place, the paste may be conveniently applied to the areas within the frame. The frame, such as wood frames, may be provided with sides that can be attached to the mold surfaces with an adhesive. The frame(s) are removed after the paster layer has been deposited on the mold surface and dried. Conveniently, the removed frames may be recycled and re-used.

[0065] Optionally, portions of the internal surface of the mold 124 that are not covered by paste layer 128 may be pre-coated with an antistick sand primer (not shown) to form an antistick layer (not separately shown). The antistick sand primer may include an alcohol-based paint. The antistick layer may be pre-coated before or after the coating paste has been applied.

[0066] The antistick material for use with sand casting steel may be zircon powder alcohol-based coating for the antisticking sand casting steel, and the coating thickness of the antisticking sand coating is 0.5 -1 mm. After the antisticking sand coating is coated, an alcohol blowtorch or other modes are used for drying the shell/mold core, and then subsequent mold closing and pouring operation is carried out, so that the smoothness of the surface of the casting is ensured.

[0067] At Stage S130, the paste layer 128 is dried, such as by heating at about 60 °C to about 120 °C in a drying device 134, to form a solid layer 132 that is attached to the internal surface 122 of the casting mold 124. If the optional antistick layer is present, the antistick layer may also be dried at the same time.

[0068] At stage S140, the mold 124 is assembled as in any known cast molding process. The assembled mold 124 defines a casting chamber 142 and includes an inlet 144 for poring a cast liquid 146, such as a metal melt or molten metal liquid, into the casting chamber 142. The casting chamber 142 of mold 124 has an internal shape selected and formed according to the desired external shape and dimensions of the cast objects to be formed. The mold 124 may a non-resuable mold, or a reusable mold, and may be made of any suitable material depending on the required conditions for the cast molding process. In some embodiments, the mold 124 is a non-reusable mold and may be a mold suitable for sand casting.

[0069] At stage S150, the cast liquid 146 is prepared and poured into the casting chamber 142 through the inlet 144. The cast liquid may be any suitable cast liquid for forming the desired cast object. For example, the cast liquid 146 may include a ferreous alloy, such as chromium and iron, a steel alloy, or other ferroalloys. In some embodiments, the cast liquid 146 may be a high-carbon ferrochrome material comprising, e.g., more than 10 wt% of chromium and about 2 wt% to about 6 wt% of carbon. The cast liquid 146 may be prepared, melted, and poured in any suitable manners as known to those skilled in the art. As depicted in FIG. 1 , a ladle 148 or any other suitable pouring container or molten material transportation device or system may be used to pour the cast liquid 146 into the mold 124.

[0070] In some embodiments, the cast liquid 146 includes iron and chromium.

The chromium content in the cast liquid may be relatively high for forming high- chromium cast iron objects. [0071] In other embodiments, the cast liquid includes a steel alloy.

[0072] The cast liquid may be smelted, such as by induction smelting. In some embodiments, the cast liquid may be smelted in a medium frequency induction smelter or furnace with an operating frequency of about 300 Hz to about 10,000 Hz.

[0073] The pouring speed of the cast liquid 146 may be controlled depending on the particular application, and may be controlled to allow the liquid level of the cast liquid in the casting chamber 142 to rise at a rate of 3.5 mm/s or higher. The pouring speed may be selected to ensure the pouring is completed while the cast liquid in the casting chamber 142 is still within the optimal temperature range, to ensure sufficient and proper filling of the casting chamber 142 of the mold 124. The optimal temperature range varies depending on the cast material. For example, for high- chromium casting iron, the temperature range may be about 1 ,500 °C to about 1 ,600 °C. By comparison, for steel, the temperature range may be about 1 ,600 °C to about 1 ,650 °C.

[0074] After the casting chamber 142 is fully filled with the cast liquid 146, the temperature of the cast liquid 146 may be in the range of 1530 °C to 1580 °C, or may be varied according to known casting or cast molding techniques.

[0075] At Stage S160, the temperature in the casting chamber 142 is lowered and the cast liquid is cooled and solidified. A cast object 162 is formed and can be taken out of the mold 124. Before removing the cast object 162 from the mold 124, the mold 124 or the cast object 162 may be subject to a conventional casting processing or treatment such as cooling and shakeout. For example, the cooled mold 124 may be vibrated to remove sand from the cast object 162 in a procedure known as shakeout.

[0076] Any excess materials, such as excess metal materials and residual sands or coating materials, on the cast object 162 may be removed in a cleaning or finishing process.

[0077] The removed cast object 162 may be further treated, such as subject to heat treatment, tempered, or further hardened. For example, the cast object 162 may be heated for austenite destabilization heat treatment. The heat-treated object may be further finished after cooling, such as by sandblasting finishing processing. The post-casting treatments to the cast objecting 162 may include any suitable or desired treatment as known to those skilled in the art and will not be detailed herein as they are not relevant to the formation of the TiC coating on the cast object.

[0078] Without being limited to any particular theory, it is expected that when the cast liquid 146 contacts the dried coating layer 132, heat from the molten metal material, such as molten iron, is transferred to the coating layer 132 and the transferred thermal energy is sufficient to trigger and promote a self-propagating high-temperature synthesis (SHS) process. The SHS process may occur throughout the pouring stage, Stage S150, when the temperature is maintained above a threshold temperature for the SHS process to continue. In the SHS process, selfpropagating titanium-carbon reactions occur at the interfacial regions of the coating layer 132 and the cast object 162. The reactions may be generally represented as: Ti + C = TiC. The reaction product is titanium carbide (TiC) or a TiC-based alloy phase, which can penetrate or extend into the surface of the cast object 162 that is in contact with the coating layer 132 during the casting process, resulting in a TiC coated surface 164 on the cast object 162. The coating mixture 104, coating paste 110, or coating layer 128/132 can thus all be considered as precursor materials for the TiC coating on the coated surface164 of cast object 162.

[0079] As a result of self-propagating reaction and molten casting liquid infiltration, composite materials of a ceramic phase and a matrix with extremely fine pores may be formed at the interfacial regions or regions adjacent to the coated paste layers. The ceramic materials can be quite hard. For example, the Mohs hardness of ceramic materials may be close to 10. The composite materials in the coating regions thus have improved wear/abrasion resistance and toughness. Molten metal infiltration during casting can also improve the compactness of the cast object. To improve fusing of the different phases during casting, the liquid level of the casting liquid can be controlled so that the liquid level rises sufficiently fast, as compared to the SHS reaction rates.

[0080] The metal components in the coating material may also participate in the reactions and form a transitional intermediate phase. The intermediate phase can effectively enhance the bonding strength between the alloy phase and the cast base material at the coated surface regions. The strength and hardness of the coated high-chromium casting iron are thus higher than those of an uncoated high- chromium cast iron. The coated surface is reinforced and has a tightly integrated structure.

[0081] As can be appreciated, because the TiC coating 164 only forms on any portion of the surface of the cast object 162 that is in contact with the coaling layer 128, the TiC coating 164 can be conveniently localized at the selected part(s) on the cast object surfaces, by selectively forming the coating layer 128 in the mold 124. The TiC coating provides increased resistance to wear and may also provide improved resistance to impact stress.

[0082] As can be appreciated, the process S100 may be suitable for localized coating of TiC on exposed external surfaces of the cast object 162, which are in contact with a relatively-easy-to-reach internal surface of the casting chamber 142 of mold 124.

[0083] In situations where an internal surface of a cast object is to be coated with a TiC coating, it may be difficult to form a coating layer on the corresponding mold surface as described above with reference to FIG. 1 . In such situations, a different method of attaching the coating materials to the mold surface may be selected and used.

[0084] For example, in a casting process S200 as illustrated in FIG. 2, the coating mixture 104 is mixed with a lubricant 202 and then compacted to form coating blocks 204 at Stage S210.

[0085] The lubricant 202 may be stearic acid or paraffin. In different embodiments, other suitable lubricants may also be used. The lubricant material may be selected to avoid bonding or adhesion of the cast object to the mold and allow easier detachment of the cast object from the mold.

[0086] The powder materials in the coating mixture 104 and the lubricant 202 may be stirred/agitated and thoroughly mixed to provide a viscous material before the viscous material is compressed and compacted. The weight ratio of the lubricant 202 and the mixture 104 may be selected depending on a number of factors. In some embodiments, the viscous material for forming the coating block 202 may have 3 wt% to 8 wt% of the lubricant 202. In some embodiments, the viscous material may contain 4 wt% to 6 wt%, such as 5 wt%, of the the lubricant 202.

[0087] In an embodiment, the viscous material for forming coating blocks 204 may be loaded into a mold 206, such as a metal mold, and compressed in the mold 206 to form the coating block 204 by a pressure forming technique, such as vibration pressure forming. The compressed block of materials is then dried to form the final coating block 204.

[0088] The forming pressure for forming the coating blocks may be about 15,000 kg/cm² or more in some embodiments, and may be increased in other embodiments as can be appreciated and determined by those skilled in the art. The compressing pressure should be sufficiently high to provide generally uniformly compressed and compact block material, which will not disintegrate when the blocks are stored, transported and affixed to the molds, and will provide generally uniform distribution of the coating mixture 104 on the mold surface so that the resulting TiC coating on the cast object has generally uniform strength, or has variable strengths that can be conveniently controlled by adjusting the block thickness.

[0089] The coating block 204 may have any desirable size or shape. For example, it may have a generally rectangular shape with a thickness of about 2 mm to about 100 mm, such as about 2 mm to about 40 mm. The thickness of the block may be varied depending on the desired surface coating properties on the resulting cast object. For example, for stronger coating surfaces, the block may be thicker; and vice versa. The edges and corners of the coating block may be rounded to provide smooth transition and avoid sharp edges and corners. The shapes of the blocks and their positions may be selected depending on the shapes of the cast object to be formed, particularly when the cast object has an irregular shape or complex structure, so that different parts or areas of the cast object will be uniformly strengthened by the TiC coating. Alternatively, the thicknesses of the blocks 204 at different locations in the mold 224 may be varied to adjust the resulting coating strengths at different parts of the resulting cast object.

[0090] At Stage S220, the coating blocks are affixed to selected locations on internal surface(s) 222 of a mold 224. Mold 224 may be a precoated sand shellmold. The shell-mold may be dried after affixing the coating blocks to the selected locations.

[0091] Blocks 204 may be affixed to the mold 224 in any suitable manner. For example, the blocks 204 may be attached to a surface of mold 224 by an adhesive. The adhesive may be an aqueous solution of a polyvinyl acetate or another polyvinyl alcohol (PVA). The adhesive may be spread over the surface of the mold 224 and the block 204 is then attached the surface by the adhesive and will be affixed to the mold 224 after the adhesive is dried. The mold 224 with the attached block 204 may be dried in a drying furnace or chamber.

[0092] Another option is to affix the block 204 to mold 224 by a mechanical device, such as a dowel pin. Dowel pins may be inserted into or otherwise provided on the coating blocks 204, and corresponding pin holes may be provided on the mold surfaces. The terminal ends of the dowel pins on the coating blocks are inserted in the corresponding pin holes of the mold to affix the coating blocks onto the mold surfaces.

[0093] At Stage S230, the shell-mold 224 is assembled to provide an enclosed casting chamber, similar to Stage S140 of process S100.

[0094] AT Stage S240, the cast liquid 146 is poured into the mold 224.

[0095] At Stage S250, the cast liquid 146 in the mold 224 is heated to perform cast molding and form the cast object 262, similar to in Stages S150 and S160 in process S100.

[0096] At Stage S260, the cast object 262 may be subject to further treatments as described above with reference to process S100.

[0097] Process S200 may be suitable for coating interior surfaces of a mold cavity, particularly in situations where there are cavities in the mold that are not conveniently accessible for forming surface coating materials as described in process S100.

[0098] Examples [0099] Example cast objects were prepared according to embodiments disclosed herein.

[00100] In the examples described below, all raw materials were obtained from commercial sources in China. The commercially obtained raw Ti and graphite powders were of 200-300 mesh, and the tungsten carbide power was of 300 or 325 mesh, unless otherwise specified below.

[00101] Example I. Sample Precursors and Their Preparation

[00102] Eight sample coating precursor materials were prepared. The ingredients of the Samples (I to VIII) are listed in Tables I and II in unit weights (parts) on the basis of dry weight of the listed ingredients. All listed materials were in powder forms. The Ti powder, graphite powder, and mixed metal powder were all 200-300 mesh, and the tungsten carbide powder was 325 mesh.

Table I. Example Precursor Materials for TiC Coating (in parts)

Table II. Mixed Metal Powders in Example Precursor Materials

[00103] Samples ICVIII were prepared as follows.

[00104] The respective metal powders for Sample were selected from commercially obtained nickel (Ni) powder, molybdenum (Mo) powder, copper (Cu) powder, cobalt (Co) powder, silicon (Si) powder, rare earth (RE) powder, magnesium (Mg) powder, boron (B) powder, and iron (Fe) powder, weighed, and mixed in the desired proportions. [00105] The mixed metal powders were mixed, agitated, and grinded in a ball mill for 20 hours to obtain thoroughly mixed metal powders of about 200 mesh.

[00106] The selected titanium (Ti) powder, graphite (C) powder, tungsten carbide (WC) powder, in the selected weight proportions, were then added to the grinded metal powder in the ball mill, and the mixed powder materials were agitated and grinded for 15 hours until the powder materials were sufficiently uniform to provide the coating precursor mixture.

[00107] Comparison Materials IC.

[00108] Comparison Materials were also prepared in a similar process as for the Sample I, but with varied weight proportions (parts) of selected ingredients to study the effects of their variation.

[00109] Comparisons IC1A and IC1 B were prepared to study the effects of varying Ti content in the precursor as compared to Sample I, so only the weight of Ti powder was varied in Comparisons IC1 A and Comparison IC1 B as compared to Sample I. Similarly, Comparison IC2A and Comparison IC2B were prepared to study the effects of varying graphite content in the precursor as compared to Sample I, so only the weight of graphite powder was varied in Comparison IC2A and Comparison IC2B as compared to Sample I. In Comparisons 1-3A and IC3B, only the weight of tungsten carbide was varied to study the effects of varying WC content. In Comparisons 1-4A and IC4B, only the weight of mixed metal was varied to study the effects of varying metal content. The ingredients of Comparisons IC1 A to IC4B are listed in Table III.

Table III. Comparison Precursor Materials

[00110] Comparison Materials II. [00111] Comparisons IC5 to IC8 were prepared similarly as Sample I but with varied weights of selected metals in the mixed metal powder. The contents of the respective metals in Comparisons IC5 and IC8 are shown in Table IV.

Table IV. Metal contents of Mixed Metals of Comparison Materials

[00112] Example II.

[00113] Each of Example Samples ICVIII and Comparisons ICIA to IC8 was tested for coating performance in casting according to the following procedure, which was an embodiment of the process S100 illustrated in FIG. 1 .

[00114] An aqueous solution containing 1 .2 wt% a polyvinyl alcohol (PVA) was obtained and used as an adhesive material.

[00115] 120 g of the sample or comparison material to be tested, 30 g of the adhesive material, and 10 g of water were mixed and stirred to form a paste.

[00116] The paste was deposited on selected portions of an internal surface of a rectangular sand coated shell mold to form a layer of the paste with a thickness of 10 mm. The portions of the mold surface not covered by the paste were covered with a layer of an antistick material. The antistick material contains zircon powders dispersed in an alcohol. The antistick layer had a thickness of about 0.5 mm.

[00117] The mold with covering layers was torched for 15 minutes with a blowtorch, and then placed in a molding furnace and heated at 200 °C for about 5 to 7 hours until the covering layers on the mold were thoroughly dried.

[00118] The mold was then assembled and used to cast molding with a high ferrochrome casting liquid as described above with references to process S100 as illustrated in FIG. 1. The casting liquid was prepared in compliance with the BTMCr27 standard/specification (see GB/T8263-1999 Abrasion-resistant White Iron Castings, published September s, 1999, and ASTM A532/A532M-93a (1999) Standard Specification for Abrasion-resistant Cast Irons, available at https://webstore.ansi.org/standards/astm/astma532a532m93a1999e1 ). The pouring temperature was about 1530 °C to 1580 °C and the casting liquid was poured using a bottom-injection technique, to avoid or reducing scouring the surface layers in the mold. The pouring speed was controlled so the liquid level in the casting chamber rose at a rising speed of about 3.5 mm/s or higher. During pouring, the coating precursor materials diffused into the adjacent casting liquid.

[00119] After the casting chamber was filled and pouring was completed, the mold was cooled, and the cast object was removed. The removed cast object had a TiC coating at the portions adjacent to the mold surface portions that were coated with the coating precursor materials.

[00120] The removed cast objects were subject to finishing treatment, and heat treatment for austenite destabilization and tempering. The heat-treated cast objects were sandblasted and grinded to obtain the finished cast objects.

[00121] The finished cast objects were tested for hardness strength with a portable Leeb hardness tester. The test results are listed in Table V.

Table V. Test Results

[00122] It can be seen from the test results that the cast objects coated with Samples ICVIII show generally smooth and flat surfaces with substantially increased hardness (averaging 67 HRC) as compared to the uncoated cast object (about 59 HRC).

[00123] However, coating with Comparison materials IC1A to IC6 all resulted in decreased hardness. While the surface hardness of the cast objects coated with Comparisons IC7 and IC8 were slightly higher than the uncoated surface, the coated surfaces exhibited significant surface defects.

[00124] Without being limited to any particular theory, it can be observed that when the Ti content in the coating material is too high (i.e. greater than 70 wt%) or too low (i.e., less than 20wt%), the resulting TiC coatings have inferior properties.

[00125] When the Ti content is too high, as in Comparison IC1 A, some Ti material in the paste layer did not react during casting, and the excess Ti material was observed to be present on the cast object surface in chunks. The coated surface was less dense. The ceramic phase in the cast object was unstable and the hardness of the surface material could be measured.

[00126] When the Ti content was too low, as in Comparison IC1 B, because insufficient Ti was present, the SHS reaction was incomplete. As a result, the surface structure of the cast object was less dense than the uncoated cast objection and had a significantly decreased hardness (52.2 HRC). The surface structure was loose and had decreased hardness. [00127] When the graphite content in the coating material is too high (greater than 20 wt%) or too low (less than 3 wt%), it could be observed that the resulting TiC coatings also have inferior properties.

[00128] When the graphite content is too high, as in Comparison IC2A, the resulting coating structure was loose, so the hardness of the TiC coating was relatively low (57.2 HRC).

[00129] When the graphite content was too low, as in Comparison IC2B, the SHS reaction was incomplete, and the resulting ceramic phase was unstable such that the hardness of the coated surface could not be measured.

[00130] When the WC content was too high (greater than 30 wt%), as in Comparison IC3A, obvious surface defects were present on the coated surface and the hardness of the coated surface could not be measured. When the WC content was too low (less than 3 wt%), it appeared that the SHS reactions were affected, and local over-burning was observed. The hardness (55.5 HRC) of the coated surface was less than the uncoated surface.

[00131] When the total mixed metal content was too high (greater than 70 wt%), as in Comparison IC4A, the resulting coated surface was porous and had obvious surface defects, with low hardness that could not be measured. When the total mixed metal content was too low (less than 3 wt%), as in Comparison IC4B, the ceramic phase and the matrix were poorly bonded or integrated, and the hardness of coated surface was low and could not be measured.

[00132] Testing results also show that the respective metal content in the mixed metal mixture could also significantly affect the coating properties. When any specific metal content was outside a certain range, the hardness of the coated surface deteriorated as compared to the corresponding example Samples ICVIII. Further, various defects were observed, which included metallurgical bonding defects, metal precipitates, surface deposits, internal pores, cold cracks, etc. These defects affected the bonding strength between the matrix and the ceramic phase in the cast object, such that the coated surface of the cast object was not hardened or reinforced. [00133] It could be observed that the mixed metal powder as a whole and its respective components and their contents all have material effects on the final surface properties of the coated surface of the cast object including its hardness.

[00134] Example III.

[00135] Example coating precursors were used to reinforce selected surfaces of cast molded pump components.

[00136] The casted components were components with an opening or port for fluid flow to flow through, such as guard plates or sheathes of slurry pumps.

[00137] A representative example cast guard plate 300 is illustrated in FIGS. 3, 3A and 3B. As illustrated in FIG. 3, the guard plates had a flow port with an outer diameter (D) of 500 mm to 1 ,500 mm, an inner diameter (d) of 30 mm to 50 mm, and a total thickness of 100 mm to 300 mm. The total weight of the cast guard plate was 50 kg to 2,500 kg. The substrate material of the guard plate was high-chromium cast iron. As illustrated in FIGS. 3A and 3B, the flow facing surface in the port of the guard plate 300 was reinforced with TiC coating 302. Guard plate 300 may be used as a front guard plate.

[00138] Other front and rear guard plates were also formed by casting as described herein. See presentative examples below in Example IX.

[00139] The coating material was prepared as follows.

[00140] 12 kg of the coating material was prepared with ball milling 7 kg of 300 mesh Ti powder, 1 .5 kg of 300 mesh graphite powder, 1 kg of 325 mesh WC powder, and 2.5 kg of 200 mesh mixed metal powder. The mixed metal powder contains 50 wt% of nickel powder, 3 wt% of molybdenum powder, 3 wt% of silicon powder, 3 wt% of rare earth powder, 1 .5 wt% of magnesium powder, 5 wt% of copper powder, 3 wt% of cobalt powder, and the balance being iron powder.

[00141] The mixed metal powder was prepared as described in Example I. The coating precursor was then prepared as described in Example I.

[00142] 12 kg of the coating precursor were mixed with 3 kg of the PVA solution described in Example I and 1 kg of water, and the mixture was stirred to form the coating paste.

[00143] Wooden frames were mounted in the sand coated molds at the portions corresponding to the surfaces of the cast object to be coated, which were areas in the cast component that were prone to failure. The paste was spread and evenly deposited within the frames at a thickness of about 10 mm. The edges of the paste layer were smoothed, and excess paste materials were removed. The wooden frames were then removed, and the edges of the paste layers were again smoothed.

[00144] An antistick primer was applied to areas of the molds that were not covered by the coating paste as described in Example II.

[00145] The cast components were then formed according to the cast molding process as described in Example II. The TiC coating on the resulting cast components had an initial thickness of 10 mm to 15 mm.

[00146] The surfaces of the cast guard plates were polished to have a roughness average (RA) of 0.8 pm.

[00147] It was observed that there were no obvious scratches and burns on the coated surfaces of the cast guard plates. The measured hardness of the finished cast guard plates with TiC coating was 67 HRC.

[00148] The cast guard plates were X-rayed to detect structural defects, and the internal and reinforcing layers of the cast guard plates appeared to be free of observable defects such as pinholes, shrinkage cavities, or looseness. The cast guard plates appeared to have good compactness.

[00149] Comparative Cast Component 11 IC

[00150] Comparative cast components were formed for comparison with the example cast components formed in Example III.

[00151] The comparative cast components were cast molded in the same manner as in Example III, except that no coating layer was provided in the molds for casting. [00152] The surfaces of the Comparative Cast Components IIIC were also polished to 0.8 Ra, and no obvious scratches and burns were observed on the surfaces after polishing. However, their measured hardness was only 58.2 HRC, lower than the hardness of Example III components by almost 9 HRC.

[00153] Example IV

[00154] Cast pipe elbows were prepared similarly as in Example III, except that the coating materials were applied as coating blocks affixed to the molds, instead of applied as paste layers.

[00155] An example cast pipe elbow 400 is schematically illustrated in FIGS. 4A and 4B. The pipe elbows had a wall thickness of 4 mm to 45 mm and an inner diameter (d) at the end face of 50 mm to 1000 mm. The angle between the end faces was 45 -160 degrees, and the radius (R) of curvature of the central axis was 50 mm - 2000 mm. The total weight of the pipe elbow was 0.5 kg to 2,000 kg. The substrate of the pipe elbow was made of a high-chromium cast iron material, and the flow impact bearing surface of the pipe elbow 400 was coated and reinforced with TiC coating 402.

[00156] The coating material had a weight of 4.5 kg, and contains 0.5 kg of 300 mesh Ti powder, 0.5 kg of 300 mesh graphite powder, 0.5 kg of 325 mesh WC powder, and 1 kg of 200 mesh mixed metal powder. The mixed metal powder contained 50 wt% of nickel powder, 3 wt% of boron powder, 1 wt% of rare earth powder, 3 wt% of silicon powder, 1 .5 wt% of magnesium powder, 5 wt% of copper powder, 3 wt% of cobalt powder, and the balance being iron powder.

[00157] The mixed metal powder was prepared as described in Example I but grinded in the ball mill for 20 hours to form powder of 300 mesh.

[00158] The coating precursor mixture was then prepared as described in Example I but only grinded in the ball mill for 12 hours to obtain the coating material.

[00159] 4.5 kg of the coating material were mixed with 50 g of stearic acid and stirred to form a viscous powder mixture.

[00160] The viscous powder mixture was loaded into a metal mold and compacted to form prefabricated block by vibration pressure forming. The wet prefabricated block was dried in the furnace at 200°C for 1 hour to solidify the block.

[00161] A PVA solution with weight ratio of PVA:water of 1 :20 was applied to the surfaces in the mold to be affixed with the coating blocks, as adhesive. The coating blocks were attached/affixed to selected surfaces by the adhesive. The mold with the attached coating blocks was dried in a furnace at 200°C for 2 hours.

[00162] The dried mold was assembled and cast molding was performed as in the process described in Example II, but in a medium-frequency induction furnace.

[00163] The formed elbows were buried in sand and stood for 2 hours, until cooled to the room temperature. The elbows were then subject to sandblasting treatment, and quickly tempered. The tempered elbows were trimmed and polished to obtain a finished elbow cast product.

[00164] The surface of the cast product was polished to 0.8 Ra. No obvious scratches and burns were observed on the elbow surfaces. The measured hardness of the elbow product with TiC coating was 69 HRC.

[00165] The casted elbow was X-rayed to detect defects and was found defect- free. The casted elbow was very compact.

[00166] Comparative Cast Product IVC

[00167] Comparative cast product IVC was prepared in similar manner as the casted elbow in Example IV, except that it was not coated with TiC coating. The cast product IVC was polished to 0.8 Ra, and no obvious scratches and burns were observed on the surface. It had a measured hardness of 61.3 HRC, lower than that of the cast elbow in Example IV by 7.7 HRC.

[00168] Example V

[00169] Example wear-resistant cast plates were prepared by a process similar to that of Example I. The cast plates had a length (L) of 10 mm to 650 mm and a width (W) of 10 mm to 600 mm. A representative cast plate 500 is illustrated in FIGS.

5A and 5B, which included a steel substrate 506, a high-chromium cast iron layer 504, and a TiC coating 502, with respective thickness of 5 mm to 40 mm, 10 mm to 145 mm, and 5 mm to 20 mm.

[00170] Other cast plates with different shapes were also prepared by similar casting process. Representative examples of these other plates are described in Example IX below and illustrated in FIGS. 13A to 15B.

[00171] 6 kg of coating material was prepared by ball milling and mixing 3.5 kg of 300 mesh Ti powder, 0.75 kg of 300 mesh graphite powder, 0.5 kg of 300 mesh WC powder, and 1.25 kg of 200 mesh mixed metal powder. The mixed metal powder contained 50 wt% of nickel powder, 3 wt% of molybdenum powder, 3 wt% of rare earth powder, 1 .5 wt% of magnesium powder, 5 wt% of copper powder, 3 wt% of cobalt powder, and iron powder as the balance.

[00172] The mixed metal power was prepared as in Example I but the average particle size of the grinded metal powder was 300 mesh. The coating precursor was then prepared from the powder materials as in Example I.

[00173] Coating paste was prepared as in Example II, with 6 kg of the coating precursor mixture, 1 .5 kg of the PVA solution, and 300 g of water. It was observed that the resulting paste had good formability and could hold form well.

[00174] The working surfaces of the molds were covered with the paste. After the paste was applied to selected surfaces of the mold, excess paste was removed using a scraper or callipers, so that the surface of the paste layer was flat and compact. A number of evenly distributed holes were formed on the paste layer, by pushing iron pins of 5 mm diameter into the paste layer, to allow the casting liquid to flow through the holes. The thickness of the paste layer varied from 5 mm to 15 mm and was selected for each particular plate depending on the desired properties and measurements of the particular plate.

[00175] The cast plates were formed in a similar casting process as described in Example II, with the following differences. The paste layer was dried at 180°C for 4-6 h. Six plates were casted at the same time with multiple pouring.

[00176] The cast plates were polished to 0.8 Ra, no obvious scratches and burns were observed on the polished surface. The measured hardness of the cast plates with the TiC coating was 69 HRC. The cast plates were X-rayed to detect defects and were found to be free of defects such as pinholes, shrinkage cavities and looseness, and have good compactness.

[00177] Comparative Cast Plates VC

[00178] Comparative cast plates VC were prepared similarly as example cast plates V, but without the TiC coating. The measured hardness of the uncoated comparative cast plates VC was 59.5 HRC, which was 9.5 HRC lower than that of the example cast plates V.

[00179] It is noted that although only rectangular shaped plates were tested. In different embodiments, the shapes and sizes of wear-resistant plates can vary and may have a square profile, a circular profile, a fan-shaped profile wear-resistant plate, an annular profile, or the like.

[00180] Examples VI

[00181] Various cast pump covers were coated with TiC coating as described above.

[00182] It was known that the commercially available conventional uncoated slurry pump covers made of white cast iron had an expected service life of about 500 hours under the operating conditions of intended application.

[00183] The cast pump covers were prepared as described in Examples I and II with the differences noted below.

[00184] Some initial TiC coated covers were prepared as in Examples I and II, except that the mixed metal powder contained 50 wt% nickel, 3 wt% molybdenum, 5 wt% copper, 3 wt% cobalt, 3 wt% silicon, and iron for the balance. That is, the metal powder for the initial coated covers did not include any rare earth, Mg or B powders.

[00185] The initial coated pump cover were observed to exhibit poor deoxidation and slag removal effects at the self-propagating combustion interface, low combustion temperature, and insufficient combustion or even no-combustion after self-propagation. As a result, the coating layer showed local, limited breakoffs, and insufficient integration between the different material layers. When the paster layers were thicker than 20 mm, breaking points were observed.

[00186] The initial coated covers were installed on a slurry pump and tested in the intended operating conditions, after 771 hours of operation, the coated covers exhibited perforation and the pump provided insufficient flow rates.

[00187] Improved pump covers were prepared according to the coating materials and processes of Examples I and II. It was observed that addition of magnesium, rare earth, and boron in the coating material improved the continuity of the combustion reactions during casting and deoxidation at the transition areas, so the resulting cast products had more reliable and stable integrated structure.

[00188] X-ray analysis showed that the improved coated pump covers were free of defects such as pinholes, shrinkage cavities and looseness, and exhibited good compactness.

[00189] The improved TiC coated pump covers were tested under the same operating conditions. Liquid leakage was found only at the uncoated regions of the sealed connection after 1080 hours of operation. That is, the expected service life was at least doubled, as compared to the conventional uncoated pump cover.

[00190] Uncoated (RSA), initial coated (RSB), and improved coated (RSC) pump covers were prepared and tested according to testing standard ASTM G65- 2004(2010), Procedure A. In particular, a dry sand/rubber wheel tester was first used to measure the amount of wear, and a dry sand/steel wheel tester was next used to measure the amount of wear. The casting liquids for all prepared pump covers included 3.34 wt% C, 22.2 wt% Cr, 1.09 wt% Mo, 0.41 wt% Ni, 0.93 wt% Si, 0.44 wt% Mn, and Fe being the balance. Before the tests, all materials were subject to heating at 1040 °C for 2 to 3 hours and then air cooled. The representative abrasion test results are listed in Table VI. The average weight lost due to wear is denoted AWL, the average volume lost is denoted AVL. The results measured by the steel wheel tester is denoted as SWAT. Table VI.

[00191] As can be seen from Table VI, as compared to the uncoated cover, the wear loss of the improved coated pump cover was reduced by 0.1206 g or 14.5 mm³, which is 56.75% in weight or 52.16% in volume, with the rubber wheel tester; and reduced by 0.101 g (32.11 %) or 10.2 mm³ (24.8%) with the steel wheel tester.

[00192] The test results showed that the TiC-coating effectively improved the strength and wear/abrasion resistance of the coated pump covers. Further, the results showed that the improved TiC-coating provided further improvement over the initial TiC-coating. In particular, the results indicated that addition of magnesium and rare earth in the mixed metal powder had significant effects on the SHS process, and the resulting coated material.

[00193] Example VII

[00194] Example cast hammers were prepared with Ti Coating.

[00195] In conventional hammers for crushing quartz stones, the hammer strike surface was embedded with hard alloy blocks during casting. The conventional hammer surfaces were uneven, and were under different local stresses, so that the embedded alloy blocks tend to partially fall off at a localized part of the surface.

[00196] The example cast hammers reinforced with TiC coating were prepared according to the process as described in Examples I and II.

[00197] It was observed that the surface of the coated hammer had a smooth surface, and the surface stress was uniform during hammering. The overall hardness of the hammer was improved, and the impact wear resistance was increased, as compared to hammers formed with the base casting material without the TiC- coating. [00198] The uncoated and coated hammers were tested by crushing quartz stones. The crushed quartz stone had a Mohs hardness of 7.3. The crushing throughput was 80 tons/hour, and the crushed stones had sizes of 10 mm to 50 mm.

[00199] The uncoated hammers exhibited large surface alloy fall-off after 13 days of testing. In comparison, the coated hammers only exhibited severe impact wear after 30 days without any fracture or falloff. The test results indicated that the coated hammers had substantially improved and strengthened working surface.

[00200] The coated hammers were X-rayed and found to be free of defects such as pinholes, shrinkage cavities, looseness and the like, and to have good compactness.

[00201] The uncoated and coated hammers were both tested for hardness as described in Example VI. The test results are listed in Table VII. The uncoated hammers are denoted as RSD, and the coated hammers are denoted as RSE.

[00202] The base casting materials (Cr, WCI, KmTBCr15-2) for both RSD and RSE contained 3.49 wt% C, 18.2 wt% Cr, 2.1 wt% Mo, 0.57 wt% V, 0.75 wt% Si, 0.43 wt% Mn, and Fe being the balance. All tested materials were subject to heating at 965 °C for 2 to 3 hours, and then air cooled.

TABLE VII

[00203] As can be seen from Table VII, as compared to the uncoated hammer, the wear loss of the improved hammer was reduced by 0.0307 g (21.33%) or 2.1 mm³ (13.38%), with the rubber wheel tester; and by 0.0968 (27.65) or 12.6 mm³ (26.92%) with the steel wheel tester.

[00204] The test results showed that the TiC-coating effectively improved the strength and wear/abrasion resistance of the coated hammers.

[00205] Example VIII [00206] Example thin wall cast products such as transporting elbow pipes were prepared according to the example process described in Examples I and II.

[00207] For example, cast elbow pipes for transporting liquid cement were prepared.

[00208] In conventional elbow pipes for transporting cement, the surfaces of existing elbow pipes were coated with a coating layer, without any shell-removal agent.

[00209] In this example, two types of cast elbow pipes were prepared according to the process described in Example II with the variation as described below. In addition to the paste layer applied to the mold surface before casting, a removal agent was also applied to the mold surface, by brushes, to facilitate the removal of the cast product from the mold after casting.

[00210] The cast pipes had thin walls of 5 mm to 10 mm thickness.

[00211] The surfaces of the Ti-C coated cast elbow pipes were smooth. During use under the same operation conditions for transporting cement, the transported fluid flow did not show obvious flow resistance and it was observed that the coated elbow pipe was less likely to exhibit localized fatigue and loss of functionality. The coated cast elbow pipes were X-rayed and found to be free of defects such as pinholes, shrinkage cavities and looseness, and to have good compactness.

[00212] During operation testing, cement slurry was conveyed through the TiC- coated cast elbow pipe, and the pipe failed after conveying 11 ,000 m³ cement slurry, due to formation of penetrating holes in the pipe wall. By comparison, the uncoated elbows with the same pipe base material failed after conveying 8,000 m³ cement slurry under the same conditions, not only due to formation of penetrating holes but also due to cracks formed in the pipe wall. Thus, the TiC-coated elbow pipe had improved lifetime by 37.5%.

[00213] Example IX

[00214] Further example cast objects were also prepared according to the processes described in Examples I, II, III or IV, but with different shapes, some of which have complex structures.

[00215] As the casting processes were similar, the details of the casting process will not be repeated. Representative example cast objects are however illustrated in FIGS. 6 to 17B, where the TiC coatings are represented by thick dark lines.

[00216] FIG. 6 shows a schematic cross-sectional view of a cast rod tooth 600 with a TiC coating 602.

[00217] FIGS. 7A and 7B show the top view and side cross-sectional view of an example front guard plate 700 with TiC coating 702. Similarly, FIGS. 8A-8B, 9A-9B, 10A-10B show respective top views and side cross-sectional views of different example front guard plates 800, 900, 1000 with TiC coatings 802, 902, 1002 respectively.

[00218] FIG. 11 B shows a top view of an example rear guard plate 1100 with TiC coating 1102, and FIG. 11A shows a side cross-sectional view thereof taken along the line 11A-11A in FIG. 1 B. FIGS. 12A and 12B show the top view and side cross-sectional view of another example rear guard plate 1200 with TiC coating 1202.

[00219] FIGS. 13A-13B show cross-sectional and top views of a wear/abrasion resistant plate 1300 with TiC coating 1302 on a high-chromium cast iron layer 1304 and a substrate 1306, similar to plate 500 but with a fan-shape. Similarly, FIGS. 14A- 14B show cross-sectional and top views of an annular shaped wear/abrasion resistant plate 1400 with TiC coating 1402 on a high-chromium cast iron layer 1404 and a substrate 1406, where the view in FIG. 14A is taken alone the line 14A-14A in FIG. 14B. FIG. 15 shows cross-sectional and top views of a circular shaped wear/abrasion resistant plate 1500 with a TiC coating 1502.

[00220] FIGS. 16A and 16B show front and top views of a cast shovel tooth 1600 with TiC coating 1602.

[00221] FIGS. 17A and 17B show front and cross-sectional views of a cast bucket tooth 1700 with TiC coating 1702. [00222] CONCLUDING REMARKS

[00223] It is to be understood that the figures are not necessarily to scale, and some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to employ the subject matter disclosed herein.

[00224] In addition, any specific numerical value listed herein includes a margin of error of +/- 10%.

[00225] It will be understood that any range of values herein is intended to specifically include any intermediate value or sub-range within the given range, and all such intermediate values and sub-ranges are individually and specifically disclosed.

[00226] It will also be understood that the word “a” or “an” is intended to mean “one or more” or “at least one”, and any singular form is intended to include plurals herein.

[00227] It will be further understood that the term “comprise”, including any variation thereof, is intended to be open-ended and means “include, but not limited to,” unless otherwise specifically indicated to the contrary.

[00228] When a list of items is given herein with an “or” before the last item, any one of the listed items or any suitable combination of two or more of the listed items may be selected and used.

[00229] Of course, the above described embodiments of the present disclosure are intended to be illustrative only and in no way limiting. The described embodiments are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.

Claims

WHAT IS CLAIMED IS:

1 . A composition for forming a titanium carbide coating on a surface of a cast object during cast molding, comprising:

(i) 20 wt% to 70 wt% of titanium (Ti) powder of 200 mesh to 300 mesh,

(ii) 3 wt% to 20 wt% of graphite powder of 200 mesh to 300 mesh,

(iii) 3 wt% to 30 wt% of carbide powder of 140 mesh to 325 mesh, the carbide powder comprising tungsten carbide or titanium carbide, and

(iv) 3 wt% to 70 wt% of metal powder of 100 mesh to 200 mesh.

2. The composition of claim 1 , comprising 30 wt% to 60 wt% of Ti powder of about 300 mesh, 5 wt% to 15 wt% of graphite powder of about 300 mesh, 10 wt% to 25 wt% tungsten carbide of about 325 mesh, and 15 wt% to 50 wt% of metal powder of 100 to 200 mesh.

3. The composition of claim 1 , wherein the metal powder consists of 0 wt% to 60 wt% of Ni, 0 wt% to 10 wt% of Mo, 0 wt% to 10 wt% of Cu, 0 wt% to 60 wt% of Co, 0 wt% to 10 wt% of Si, 0 wt% to 10 wt% of a rare earth, 0 wt% to 5 wt% of Mg, 0 wt% to 5 wt% of B, and Fe.

4. The composition of claim 1 , wherein the metal powder consists of 0 wt% to 60 wt% of Ni, 3 wt% to 10 wt% of Mo, 5 wt% to 10 wt% of Cu, 2 wt% to 60 wt% of Co, 1 wt% to 3 wt% of Si, 1 wt% to 3 wt% of a rare earth, 1 wt% to 5 wt% of Mg, 1 wt% to 3 wt% of B, and Fe.

5. A method of cast molding for forming a cast object comprising a titanium carbide coating on a surface of the cast object with the composition of claim 1 , the method comprising: attaching a precursor material comprising the composition to an internal surface of a mold; casting a cast liquid in the mold to form the cast object, wherein the casting also causes the precursor material attached to the internal surface of the mold to form a coating comprising titanium carbide (TiC) on a corresponding surface of the cast object adjacent to the internal surface of the mold. The method of claim 5, wherein the attaching comprises forming a paste comprising the precursor material, a binder, and water; and covering the internal surface of the mold with the paste, wherein a weight ratio of the precursor material to the binder and to water in the paste is 1 : (0.005 - 0.03) : (0.3 - 0.4). The method of claim 6, wherein the binder comprises a polyvinyl alcohol. The method claim 1 , wherein the attaching comprises forming coating blocks comprising the precursor material and a lubricant; and affixing the coating blocks to the internal surface of the mold. The method of claim 8, wherein said affixing comprises securing the coating blocks in position with dowel pins. The method of claim 8, wherein the precursor material and the lubricant are mixed and compressed under a pressure of 15,000 kg/cm² to form the coating blocks. The method of claim 8, wherein the lubricant is a stearic acid or paraffin wax, the coating blocks comprising 3 wt% to 8 wt% of the lubricant and having a thickness of 2 mm to 100 mm. The method of claim 11 , wherein the thickness of the coating block is 2 mm to 40 mm. The method of claim 5, comprising forming an antistick layer on a selected portion of the internal surface of the mold, wherein the antistick layer comprises an alcohol-based paint. The method of claim 5, wherein the precursor material is attached to one or more selected portions of the internal surface of the mold. The method of claim 5, wherein the cast liquid comprises (i) iron and chromium or (ii) a steel alloy. The method of claim 5, wherein the mold comprises a shell mold pre-coated with molding sand. The method of claim 5, comprising mixing (i)-(iv) of the composition in a ball mill for 1 hour to 24 hours to form the precursor material. The method of claim 6, wherein the internal surface of the mold is covered by a layer of the paste having a thickness of 1 mm to 30 mm. The method of claim 18, wherein the thickness of the layer of the paste is 3 mm to 20 mm. The method of claim 5, further comprising treating the cast object to harden the cast object. A cast object produced according to the method of claim 5, comprising: a body comprising (i) chromium and (ii) iron or steel, and having a coated surface coated by the coating comprising TiC and an uncoated surface, wherein the exposed surface has a first hardness of 35 to 65 HRC, and the coated surface has a second hardness being 3 to 8 HRC higher than the first hardness.