PL238518B1 - Method for producing three-dimensional objects on the basis of three-component phases of TiAIN system - Google Patents

Description

Description of the invention

The subject of the invention is a method for the production of three-dimensional objects based on the ternary phases of the TiAlN system.

Alloys based on titanium-aluminum intermetallic phases have been known for several decades. They are characterized by low density, high strength and stiffness, sufficient hardness and strength up to about 700 ° C (depending on the alloy composition) and heat resistance up to about 500 ° C (depending on the alloy composition). Due to these properties, they can replace titanium alloys and nickel-based alloys in space and aviation applications, reducing the weight of the products. The problem, however, is the high brittleness of these alloys at room temperatures. This causes damage to machine parts, e.g. compressor blades, before they heat up to operating temperature due to friction with gas particles or the temperature of the operating gas itself.

The solution to the problem of brittleness at room temperature is to add nitrogen to the alloy chemistry. The TiAlN and / or Ti2AlN phases formed then have a higher yield point at room temperature (compared to TiAl phases), and also show better heat resistance and hardness (up to about 800 ° C) and resistance to abrasion. So far, these phases have been used in the form of thin films obtained by PVD (physical vapor deposition) methods, used to cover cutting tools, such as milling cutters or multi-edge cutting inserts, as described in patent publications US20150211105A1 and DE 102012107129A1 or precision tools glass forming as shown in the CN patent application 102329081A. However, these techniques do not allow the object to be obtained in a massive form, thus ruling out many applications of the alloy.

The method of producing a material consisting of the Ti2AIN phase in massive form, using the SPS (Spark Plasma Sintering) technology, described in the patent application WO2014104461A1, is known. According to this application, the material containing the Ti2AlN phase is produced by mixing the Ti, Al and TiN powders in a 1: 1: 1 ratio and subjecting the powder simultaneously to pressure and current pulses.

The Japanese patent application JP2007131493 describes a method of producing massive AlTiN material. According to this method, Ti and Al powders are mixed and then preformed. The pre-formed material is then subjected to a high temperature treatment under a defined pressure in a nitrogen atmosphere. A powder is prepared from the material thus obtained, which is then subjected to another two more shaping and treatment under nitrogen atmosphere. The powder obtained after the third stage is sintered into a massive AlTiN material.

To date, no information has been published about attempts to produce massive AlTiN objects by additive methods such as the selective laser remelting technology of the present invention.

Methods of additive manufacturing of materials are currently very popular. This is mainly due to the possibility of quick production of objects without the need to make molds or stamps, which is associated with significant time savings and reduces the cost of the project. In addition, additive methods are irreplaceable in the case of the need for unit production, e.g. in medical applications (endoprosthesis components adapted to a specific patient) and complex geometry (cell scaffolding). These methods also have a number of other advantages.

One of the most important advantages of additive methods is their eco-friendliness. The raw material can be used almost 100% lossless. Compared to standard manufacturing techniques, the losses associated with post-process processing, e.g. machining, are significantly or completely reduced as the model geometry is assigned to the object already in the manufacturing process. Another advantage is the ability to produce materials that cannot be produced by conventional methods.

The essence of the selective laser remelting process is a repeated series of activities consisting in covering the working table with a layer of melted powder, smelting it with a laser beam in appropriate places, determined using the CAD model, and then lowering the working table and repeating these activities. Depending on the construction of the device, the surface of the working table and the maximum dimension in the axes may be different and determine the maximum dimensions of the manufactured element. The machines also enable the heating of the work table, which is used for maintenance purposes

At a temperature above the plasticization of the material. Due to the nature of the process, it is necessary to use a protective atmosphere of an inert gas. This protects the produced material against oxidation, and also enables convective heat exchange by blowing gas into the laser influence zone. The essence of the selective beam melting device (EBM - Electron Beam Melting) is analogous, but instead of a laser beam, an electron beam is used and the process is carried out in a vacuum.

There are known examples of the preparation of the TiAl alloy discussed above by selective laser remelting, described in the patent publication DE 102012206125A1, where the method was used for the production of low pressure turbine blades. This method uses preheating of the already partially produced product with induction heat and then continuing the process in a protective gas atmosphere with an amount of impurities of no more than 100 ppm of oxygen, nitrogen and water vapor. Such a gas can be, for example, helium.

Laser nitriding of surfaces is known. This method is described, inter alia, in the patent description US5290368A, however, so far it has been used to saturate the surface of an already formed object with nitrogen, and not to remelted layers in additive methods constituting its core.

There is known from the patent publication CN103846438 a method for producing three-dimensional objects based on the TiAlN phase, mainly from titanium and aluminum nitride powder (or from titanium and a mixture of aluminum nitride + titanium nitride). In the cited document, the proposed solution relates to the production of three-component phases from titanium nitride in the form of a coating or layer of three-dimensional objects, and not as in the present invention in the form of massive, solid objects. The diffusion processes occurring during melting between titanium nitride and aluminum are significantly different from the diffusion processes occurring between aluminum nitride and titanium during their melting, for example due to their thermal stability and have an impact on the products produced.

The method disclosed in CN103846438 for producing a TiAlN metal-ceramic composite object, which comprises the steps of mixing and preparing titanium nitride powder and metal-aluminum powder according to a ratio; sieving the homogeneously mixed composite powder, then adding to the matching mold and paving evenly; placing the mold in a hot-press sintering furnace and sintering with an inert gas at a temperature of 650-1000 ° C and a pressure of 40-50 MPa; stopping heating after insulating and holding pressure for 2-3 hours; processing the sintered composite object according to the drawing to obtain the finished product. According to the method provided by the invention, the technologies can be improved to obtain a TiAlN composite body with better performance.

In the case of the production of solid multiphase materials, its phase composition is of significant importance for the functional parameters of the produced material. In the additive method, the powders used in the process may react differently with each other depending on process parameters such as power and energy density. These parameters therefore have a significant influence on the phase composition of the material. The microstructure of the material, i.e. the size, distribution and crystallographic orientation of the grains, is also important for the functional properties.

The aim of the invention was to develop a method for the production of three-dimensional objects based on the three-component phases of the Ti-Al-N system.

The subject of the invention is a method for the production of three-dimensional objects based on three-component phases of the TiAlN system, characterized by the fact that the object is produced by an additive method consisting in fusing successive layers of the alloy material with a laser beam or an electron beam in an inert gas atmosphere with the addition of nitrogen, where a mixture is used as the alloying material. at least two powders selected from: Ti, Al, TiN and AIN, previously homogenized by mechanical synthesis at a temperature of 15-30 ° C for 5 to 30 hours, with the proportion of nitride powder not less than 5 atomic% and the process is carried out with a laser power in the range of 20-500 W, a laser beam feed rate of 10-1000 mm / s, a distance between successive paths in the range of 20-200 gm, a layer thickness in the range of 20-60 gm.

Preferably nitrogen is added in an amount of at least 5 vol.%.

Preference is given to using powders with an average particle size in the range 10-120 gm.

Preferably, the powder mixture is previously spheroidized in an inert gas and / or a nitrogen atmosphere.

PL 238 518 B1

Preferably, each layer is subjected to at least two laser or electron beam remelting during the manufacturing process. Preferably, the object after the selective remelting process is subjected to a hot isostatic pressing process.

The protective gas prevents oxidation of the material during the process, while the addition of nitrogen increases the amount of nitrogen-rich phases relative to the starting powders. Increasing the share of nitrogen in the atmosphere allows you to reduce the share of nitrides, because part of the nitrogen needed for the process comes from the atmosphere. In this way, about 5-10% of the nitride can be replaced with a suitable metal powder.

Giving the powders a spherical shape that is favorable in the process, increases the flowability of the powder. Mechanical synthesis consists in high-energy mixing of powders in tightly closed containers with ceramic balls. During the process, the powder particles combine and crumble many times, thanks to which the final powder is well homogenized. The preliminary mechanical synthesis step is preferably carried out in high energy mills under an inert gas atmosphere.

The method according to the invention makes it possible to obtain massive objects based on the three-component phases of the Ti-Al-N system, characterized by high heat resistance, corrosion resistance and heat resistance, good mechanical properties and plasticity as well as very high abrasion resistance.

In the process according to the invention, both the high-melting TiN or AIN phase and the relatively low-melting Ti or Al matrix are melted. Quick cooling of a small smelting area, the so-called laser puddle, creates a fine microstructure with good strength properties (high strength and hardness) with low brittleness. This distinguishes the method according to the invention from the known SPS synthesis, in which the structure of the produced material is similar to the initial structure of the starting powders, and sometimes grain growth may also occur. Consequently, the materials obtained by the known SPS method have poorer mechanical properties.

The method according to the invention allows to influence the obtained phase composition of the object and its microstructure by changing the process parameters, i.e. power and energy density.

Increasing the energy density causes the decomposition of AIN with the formation of ternary phases from the Ti-Al-N system, while at lower energy densities, the material exhibits the features of a composite with a titanium matrix, reinforced with aluminum nitride (AIN). In any case, however, the Ti-AIN composite obtained by the method according to the invention has high mechanical properties and high hardness, and is also characterized by high adhesion of strengthening particles due to the possibility of chemical bonding with the matrix through the transition phases from the Ti-Al-N system.

The introduction of bound nitrogen in the powder allows to achieve better mechanical properties and solves the problems associated with the use of TiAl alloys. An additional advantage of the presented method is the introduction of nitrogen into the working atmosphere, which reacts with the surface of the object during the process. This allows the use of smaller amounts of nitride powders, which are more expensive than Ti and Al powders, and thus reduce the cost of the manufactured object.

The object made by the method according to the invention is saturated with nitrogen in its entire volume, in contrast to the methods known so far, where only the surface is nitrided.

The method allows to obtain an object with almost any geometry (limited only by the diameter of the powder melting beam), therefore it can be used in the production of various structural elements and tools, which require low specific weight, high strength and heat resistance.

The method according to the invention is presented in more detail in the examples.

P r z k ł a d 1

A powder with the nominal composition of Ti: 85%, AIN: 15 atomic% was prepared from metallic titanium powder with an average particle size of 35 μm and aluminum nitride powder with an average particle size of 11 μm. The powder was mixed in a rotary mill for 10 h and dried in a vacuum dryer for 72 h. The prepared raw material was selectively smelted in a Realizer SLM-50 device equipped with a 120 W Nd: YAG laser in an argon atmosphere. The layer thickness was 50 µm. The speed of the laser beam was set at 125 mm / s with a path width of 50 µm and a laser power of 25 W. The paths were made successively. The material thus produced is characterized by a fragmented dendritic microstructure and a high hardness above 600HV0.2.

Fig. 1 is a photograph taken with a Hitachi TM 1000 Scanning Electron Microscope showing the microstructure of the material obtained in Example 1. Magnification of 3000x.

PL 238 518 B1

P r z k ł a d 2

A powder was prepared with the nominal composition of Ti: 85%, Al: 5%, A1N: 10 atomic% and a particle size below 80 μm. The powders were homogenized in a rotary mill. The resulting starting powder was selectively smelted in a Realizer SLM-50 in an atmosphere of a mixture of 25% nitrogen and 75% argon. The laser power was set at 30 W, the beam speed was set to 100 mm / s, the layer thickness was 50 μm and the distance between successive tracks was 60 μm. The material obtained had a hardness above 600HV0.2 and a fine-grained, dendritic structure analogous to that of the material produced in Example 1.

Fig. 2 is a photograph taken with a Hitachi TM 1000 Scanning Electron Microscope showing the microstructure of the material obtained in Example 2. Magnification of 3000x.

P r z k ł a d 3

The powder with the nominal composition of Ti: 70%, AIN: 30% by weight and particle size below 70 μm was prepared from metallic titanium powder and aluminum nitride powder and was subjected to mechanical synthesis in a high-energy mill for 24 hours and plasma spheroidization in nitrogen atmosphere. The resulting raw material was selectively smelted in the Realizer SLM-50 device in an argon atmosphere. The laser power was set at 20 W. The layer thickness was 50 µm, the distance between successive tracks was 50 µm and the laser beam was fed at a speed of 150 mm / s. The three-dimensional object thus produced, and then subjected to hot isostatic pressing at a pressure of 150 MPa and a temperature of 1200 ° C, which allowed to achieve a density above 99% of the theoretical density. The microstructure of the material consisted of a titanium matrix in which the reinforcing phase were AIN particles bound to the matrix through the Ti3AIN / Ti2AIN transition phases.

Fig. 3 is a photograph taken with a Hitachi S3500N Scanning Electron Microscope showing the microstructure of the material obtained in Example 3. Magnification 3500x.

Claims (6)

Patent claims 1. A method of producing three-dimensional objects based on three-component phases of the TiAlN system, from metal powders and metal nitrides, characterized in that the object is produced by an additive method consisting in fusing successive layers of the alloy material with a laser beam or an electron beam in an inert gas atmosphere with the addition of nitrogen, where as the alloying material, a mixture of at least two powders selected from: Ti, Al, TiN and AIN, previously homogenized by mechanical synthesis at a temperature of 15-30 ° C for 5 to 30 hours, with no nitride powder content less than 5 atomic% and the process is carried out with a laser power in the range of 20-500 W, a laser beam feed rate of 10-1000 mm / s, a distance between successive paths in the range of 20-200 μm, a layer thickness in the range of 20-60 μm. 2. The method according to p. 2. The process of claim 1, characterized in that nitrogen is added in an amount of at least 5 vol.%. 3. The method according to p. The process of claim 1, wherein the powders are used with an average particle size in the range 10-120 µm. 4. The method according to p. A process as claimed in claim 1, characterized in that the powder mixture is previously spheroidized in an inert gas and / or a nitrogen atmosphere. 5. The method according to p. The method of claim 1, characterized in that each layer is subjected to at least two laser remelting or electron beam remelting during the manufacturing process. A method according to any of the preceding claims, characterized in that the object after the selective remelting process is subjected to a hot isostatic pressing process.