WO2020245645A1

WO2020245645A1 - A green body composition and functional gradient materials prepared thereof

Info

Publication number: WO2020245645A1
Application number: PCT/IB2019/059435
Authority: WO
Inventors: Venkata Sundeep SEESALA; Santanu DHARA
Original assignee: Indian Institute of Technology Kharagpur
Priority date: 2019-06-05
Filing date: 2019-11-04
Publication date: 2020-12-10
Also published as: EP3980389A4; EP3980389A1

Abstract

The present invention relates to a green body composition for use in fabrication of functionally gradient materials and metal ceramic composites. The functional gradient materials of the present invention can be machined to a near net shape in the green stage and have applications in biomedical devices, prosthetics and implants, Defense equipment, aerospace, automobile components and the like.

Description

A GREEN BODY COMPOSITION AND FUNCTIONAL GRADIENT MATERIALS PREPARED THEREOF

Cross reference to related application: The present application claims priority of Indian patent application No 201931022298, fded on June 05, 2019. The entire content of the aforementioned application is specifically incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a green body composition for use in fabrication of functionally gradient materials and metal ceramic composites to be used in prosthetics, implants and other such applications.

BACKGROUND OF INVENTION

Bone bonding and osseointegration are the key requirements for the materials in the area of dental and orthopedic implant application. Existing implants are not robust enough to mimic in-vivo load transfer mechanics at the implant tissue interface due to mismatch of the modulus and structural attributes. The metal and ceramic implants available in the market (having uniform strength and modulus) causes bone resorption due to insufficient bone bonding and uneven load transfer to the surrounding bone which is resulted in loosening of the prosthesis. Interconnected porosity in the bone contact area would facilitate bone ingrowth and bonding eventually increasing tissue-material interaction area thereby reduction in stress shielding. However, the technique currently used is physical vapor deposition of metal on a porous replica that is time consuming, costly, requires skilled operators and high vacuum conditions.

Modulus mismatch is also an important cause of implant failure, especially in dental implants, as most of the implants available are either metallic or ceramic with uniform physical properties. However native skeletal tissues are hybrid composite with changing physico-mechanical properties as per the site specific anatomical requirement. For example, the teeth have two parts, the crown has enamel with high modulus and root has dentin with low modulus. Moreover, the supporting alveolar bone has outer cortical part and inner trabecular part with gradually increasing porosity and decreasing modulus. In orthopedic implants like hip and knee implants, along with above reasons, constant relative motion of the articular surfaces and the associated wear and tear also decrease the life of implants. Further, the metallic or polymer wear debris may cause systemic complications and inflammation.

The all ceramic dental implants and crowns have considerable rate of catastrophic failure arising from brittle nature of ceramics. Also machining of sintered ceramic is known to cause surface micro-defects thereby decreasing the fatigue strength and the fracture toughness. The PFM (Porcelain Fused to Metal) prosthetic crowns and bridges have high rate of cohesive failure at the metal-porcelain junction due to abrupt change in modulus from metal coping to porcelain veneer.

All these drawbacks can be addressed by forming functionally gradient implants or by combining dissimilar materials like metal and ceramic with a composite intermediate layer into a single component. Also ceramics and their composites display improved physical properties like surface hardness and tribology to reduce wear debris. Moreover, the ceramic wear debris is inert compared to metal. Further the composite of ceramic with metal will have increased malleability and machinability without loss of strength.

Joining directly dissimilar materials like metal and ceramic in single component is difficult due to abrupt change in the sintering temperatures, modulus mismatch and thermal expansion co-efficient. Bonding and shaping in green stage requires uniform mixture and highly loaded slurries which can be laminated with relative ease. Processing Metal Matrix Composites, Ceramic Matrix Composites and Cermets into different shapes requires high initial investment especially for reactive/oxidation prone materials. Aqueous environment or atmospheric oxygen facilitates oxidation of the metal/ ceramics precursors during their processing. Fabrication of dense in combination with porous components with complex shapes are very challenging for metals/ceramics and their composites.

Conventional implants were made with porous part for bone ingrowth, but the procedure involved is physical vapor deposition (PVD) which is time and energy consuming with low output. CN 001814838 A relates to a metallic ceramic material composed of TiC, TiN and metallic adhesive phase in the following composition: C 0.04-16.04%, Ti 60.07-67.07%, Ni 9.00-11%, Mo 7.5-12.50% and N2 1.60-5.20%. This invention also discloses a molding technology of said material including: preparing an adhesive, obtaining raw stocks by injection molding, degreasing to the raw stocks, sintering and post treatment.

US 10022792 B2 relates to a process of dough forming of polymer-metal blend suitable for shape forming.

DE 10019447 A1 relates to a binding agent for inorganic material powders for producing metallic and ceramic moulded bodies. The binder comprises a mixture from bl from 80 to 99.5% by weight of a polyoxymethlene homopolymer or copolymer B l and b2 from 0.5 to 20% by weight of a polymer system B2 which is not miscible with B l and comprises b21 from 5 to 100% by weight of polytetrahydrofuran B21 and b22 from 0 to 95% by weight of at least one polymer B22 of C2-8-olefms, vinylaromatic monomers, vinyl esters of aliphatic Ci-₈-carboxylic acids, vinyl Ci-₈-alkyl ethers or Ci-12-alkyl (meth)acrylates.

CN 104057089 A discloses a Metal, ceramic powder and polymer mixture used for manufacturing metal and ceramic products and method for removing polymer from moldings by acid catalysis.

US 9945012 B2 discloses metal matrix composites (MMCs) and methods of forming MMCs, and in particular to the use of calcium to improve integration of ceramics in aluminum containing metal matrices.

EP0639540A1 discloses a process for manufacturing metal and/or ceramic sheets obtained by powder sintering is described, comprising the following successive stages: a) preparation of at least one compound of metal and/or ceramic powders; b) extrusion of the compound to the required section and length; c) thermoforming of the extruded material by direct compression; d) pyrolysis of the thermoformed article thus eliminating substantially the polymer content and obtaining a semi-finished metal and/or ceramic sintered product.

There are few literature available for making cermet of aluminum oxide and titanium powder through spark plasma sintering of powder compacts and cytocompatibility was proved for these samples [. Reference : Tomoyuki Fujii, Keiichiro Tohgo, Masahiro Iwao, Yoshinobu Shimamura Fabrication of alumina-titanium composites by spark plasma sintering and their mechanical properties, Journal of Alloys and Compounds 744, 759e768-2018. C mentine Madec et al, Alumina-titanium functionally graded composites produced by spark plasma sintering, Journal of Materials

Processing Tech., 254. 277-282 -2018] There is no significant literature on shape forming though this process for relatively bigger samples.

US6344078B1 relates to a binder system for use in the formation of ceramic or other powder-formed greenware comprising a binder, a solvent for the binder, a surfactant, and a component that is non-solvent with respect to the binder and solvent. The non-solvent component exhibits a lower viscosity than the solvent when containing the binder and comprises at least a portion of an organic liquid having a 90% recovered distillation temperature of no greater than about 225° C. and more preferably less than 220° C. Also disclosed is a process of forming and shaping plasticized powder mixtures and a process for forming ceramic articles utilizing the binder system. However, solvent and nonsolvent parts are immiscible and also it has higher solvent to non-solvent ratio (>1) which makes the concentration of the binder in the solvent system very dilute. Further the aqueous based binder system mentioned in the patent US6344078B 1 would oxidize the reactive metal powders like titanium and magnesium due to contact with water. This will disturb the dimensional stability of our Metal ceramic composites and Functional gradient materials

The main problem required to be solved is the“absence of implants with gradient physical and mechanical properties to become more suitable to the purpose of implantation” in terms of even load transfer to the bone and inert/reduced wear debris from friction. To achieve this, main gap in the processing and shaping technology is the absence of a simple and flexible processing route to make homogeneous mixture of metal and ceramic powders into complex shapes. This is due to the difference in density and surface properties of the powders effecting the stability of the suspensions, which needs to be addressed. There is a long felt need to develop a composition and method for making functionally gradient materials and metal ceramic composites to be used in prosthetics, implants and other applications. The present inventors have surprisingly developed a composition and method which ameliorates the aforesaid shortcomings of the prior art.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a green body composition for use in the fabrication of functionally gradient materials.

It is an object of the present invention to provide a green body composition for use in the fabrication of functionally gradient materials which can be machined to a near net shape in the green stage.

It is another object of the present invention to provide a functional gradient material with improved and tailorable physical properties like strength, modulus, fracture toughness and tribology due to combination of different materials and variable porosity.

It is another object of the present invention to provide a functional gradient dental implant or orthopedic implant.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a green body composition for use in fabrication of a functional gradient material.

According to another aspect of the present invention there is provided a process for preparation of a green body.

According to yet another aspect of the present invention there is provided a functional gradient material and method of its preparation.

According to yet another aspect of the present invention there is provided a functional gradient dental implant or orthopedic implant.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings wherein:

Figure-1 illustrates a flow-diagram of process of preparation of a functional gradient material from the metal, ceramic and metal-ceramic composite green body by 2 methods: a. functional gradient formation in same component b. functional gradient formation by machinable blanks.

Figure-2 illustrates a photographic image of functional gradient block made from titanium and alumina with composite middle layer (a) after drying and (b) after sintering

Figure-3 illustrates a micro CT image of sintered titanium with solid over porous layers.

Figure-4 illustrates a photographic image of porous Ti6A14V-Al₂C)₃ composite block,

Figure -5 illustrates a photographic image of a composite block machined to implant.

Figure-6 illustrates photographic image of a porous + solid sandwich composite block

Figure-7 illustrates photographic image of a machined Ti6A14V-Al₂0₃ composite

Figure-8 illustrates a micro-CT image of machined Ti6A14V-Al₂0₃ composite

Figure-9 illustrates (A) (B) (C) SEM images of Ti6A14V-Al₂0₃ composite at 1.5KX, 5KX, 25KX

Figure-10 illustrates extruded porous and solid green T16AI4V-AI₂O3 composite. Figure-11 illustrates extrusion graph of porous CERMET dough.

Figure-12 illustrates XRD of T16AI4V-AI₂O₃ composite.

Figure-13 illustrates a photographic image of porous + solid sandwich ceramic blocks Figure-14 illustrates a micro CT image of sandwich porous and solid ceramic Figure-15 illustrates a micro CT image of extruded porous ceramic.

Figure-16 illustrates a ceramic block machined to dental bridge.

Figure-17 illustrates a green ceramic molar crown CNC machining. Figure-18 illustrates photographic image of a green molded titanium sheet Figure-19 illustrates photographic image of a titanium sheet for machining

Figure-20 illustrates a green magnesium block for machining.

Figure-21 illustrates various configurations (a, b, c, d, and e) of a dental implant with functional gradient design and variable elastic modulus.

Figure-22 illustrates a composite root implant of titanium alloy and alumina, as sintered a) micro-CT image b) photographic image.

Figure 23 illustrates a hip implant composed of a functional gradient material according to present invention. Figure-24 illustrates a SEM image which shows different layers in functional gradient block (a) Ti6A14V (b) Alumina (c) Ti6A14V+Alumina composite.

Figure-25 illustrates a mixture with varying solvent to non-solvent ratio. (a)Alumina mixture with solvent to non-solvent ratio >1.0 (b)Alumina mixture with optimized ratio 0.2 to 0.6 (c) Bar extruded from optimized mixture (d) Bar extruded from alumina mixture with solvent to non-solvent ratio <0.2 showing surface defects

Figure-26 illustrates (a) Porous alumina sponge with ~95 vol % porosity after sintering

(b) Green porous titanium sponge. The green mixture of (a) pure alumina (b) pure Ti6A14V was coated on the struts poly urethane sponge. The viscosity of the mixture was decreased by increasing the solvent to non-solvent ratio from 0.6 to 1. This made the mixture thin enough to be coated on to the struts.

Figure-27 illustrates the green mixture of Solid-porous bilayer structure made of CERMET of 50 wt.% of Ti6A14V and 50 wt% of Alumina. Porous layer was made by coating the mixture on struts of polyurethane sponge after increasing the solvent to non solvent ratio from 0.6 to 1. Both porous and solid layers were made separately and attached together in green state. They can be sintered together to obtain final bilayer structure.

Figure-28 illustrates Extrusion 3D printed (a) CERMET (b) Pure Alumina after printing

(c) Pure Alumina after sintering DETAILED DESCRIPTION OF THE INVENTION

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the scope of the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term“comprises/comprising” when used in this specification is taken to specify the presence of stated features, steps or components but does not preclude the presence or addition of one or more other features, steps, components or groups thereof.

The term“ green body” as used herein means moulded, unbumed (unsintered) compositions that are bonded via a polymer binder. The green body is then fired/sintered in a kiln to produce a strong, vitrified object.

The term‘ functional gradient material” as used herein means a material having a gradient of physical and mechanical properties for e.g. modulus, density, surface properties and porosity. Along with these properties the material can also be different in a green and sintered body, for e.g. metal on one side and ceramic on other side joined in between by composite/cermet. (Reference to the fig-2 Functional gradient block made from titanium metal and alumina ceramic with titanium + alumina composite middle layer)

The term “ Near net shape” as used herein is an industrial manufacturing technique which implies that the initial production of the item is very close to the final (net) shape, reducing the need for surface finishing.

The term“ non-solvent” as used herein means a substance incapable of dissolving a given component of a solution or mixture. The non-solvent is with respect to the binder and powder materials only. With respect to solvent the non-solvent is miscible or it can form a homogeneous phase.

The term “3D printing” or“ additive manufacturing” as used herein means a technology that allows physical components to be made from virtual three-dimensional (3D) computer models by building the component layer-by-layer until the part is complete. In comparison with subtractive manufacturing processes, in which one starts with a block of material and removes away any unwanted material (either by carving it by hand or by using a machine such as a CNC machine) until one is left with the desired part, additive manufacturing starts with nothing and builds the part one layer at a time by ‘printing’ each new layer on top of the previous one, until the part is complete. 3D printing has emerged as a solution to shorten the product development cycle, achieve the flexibility to manufacture small batch sizes, and perform manufacturing of complex designed components at a low cost.

The present invention relates to a method and composition for making functionally gradient materials and metal ceramic composites to be used in prosthetics, implants and other such applications.

The functionally gradient materials and metal ceramic composites are formed of a novel green body composition comprising metal, alloy, ceramic and/or their blends in the powder form, a non-aqueous hydrophobic thermoplastic polymer binder, a solvent and non-solvent system. The thermoplastic polymer is at a higher loading concentration of solvent and the solvent-nonsolvent combination is present at a particular ratio.

The resulting pastes of different powder proportions can be laminated to form functionally gradient material which can be machined to near net shapes. The same paste can also be made porous by introducing sacrificial spacer material which is soluble in non-solvents of polymer binder, so after drying the component can be treated with the respective non-solvent to remove spacer or in another method by coating onto an open porous poly urethane foam or sponge which is non-soluble in both solvent and non solvent and removal of said spacer by heat treatment at temperature below 600°C.

Now the component is ready for drying and sintering. This is possible only because, of same solvent-binder composition and powder loading used in all different material layers, which might be difficult with other methods.

There was no prior art found in literature search regarding formation of porous/porous-solid sandwich made of metal ceramic composite through powder processing routes using polymer binder.

In the prior arts referring to forming functional gradient materials, reported literature only suggests conventional method of powder compaction in different layers with gradient compositions followed by sintering. This method does not give the flexibility of shape forming before sintering. However, machining after sintering would be highly inefficient due to superior physical properties of these materials once sintered.

In prior arts referring to forming porous green bodies and porous/solid bilayers of the metal powders or ceramic powders, particle packing density in the porous body and solid body was not matching which resulted in differential shrinkage and delamination at the porous solid interface. Further during sintering, when a different binder is used for solid and porous mixtures, the binder burnout temperature varies in both layers and eventually particle packing would be disturbed in the layer having earlier binder burnout.

The present invention utilizes a non solvent part with respect to binder and powder only, but not with respect to solvent. Unlike in the patent US6344078B1 where solvent and nonsolvent parts are immiscible, the present invention uses a highly miscible solvent-nonsolvent system. Further non-solvent part has higher viscosity than the solvent. This miscible solvent + nonsolvent combination allows the overall mixture to be a densely packed body but having lower yield strength required for molding into shapes, extrusion 3D printing, and introducing sacrificial spacer particles.

Further as understood from the composition disclosed in the patent US6344078B1, has higher solvent to non-solvent ratio (>1) which makes the concentration of the binder in the solvent system very dilute. However, binder system used in present invention would be very concentrated as 1 part of binder requires only 4 parts of solvent + nonsolvent mixture and the solvent to nonsolvent ratio would be in decimals from 0.20 to 1.0. Further in the present invention, all parts of the solvent and non-solvent mixture are 99% recoverable by collecting the vapors obtained during drying of the final mixture at 50°C - 80°C in vacuum chamber. The collected vapor mixture can be further separated into its components by fractional distillation at temperatures below 195°C and reused. This is in contrast to the patent US6344078B 1 where only a portion of organic liquid in the non-solvent is 90% recovered at 220° C - 225°C. Hence process of present invention is more efficient and eco-friendly than US6344078B1. Further the aqueous based binder system mentioned in the patent US6344078B 1 would oxidize the reactive metal powders like titanium and magnesium due to contact with water. This will disturb the dimensional stability of our Metal ceramic composites and Functional gradient materials. However, the present invention uses a non aqueous based binder system which would coat the reactive metal powders protecting them from oxidation, thereby enhancing the shelf life of the green bodies.

Further, unlike US6344078B 1 where the binder resides at the interface between solvent and non-solvent, binder in the present invention resides completely in the solvent and coats the particles evenly in densely packed state. The dense packing of particle ensures minimal shrinkage on setting, high green strength for machining, good dimensional stability and retaining of finer details on sintering. The working time of the mixture can also be controlled from few minutes to hours depending on the setting agent and ambience. The Biomedical implants made of the functional gradient materials of the present invention are near net shaped for the first time in green stage (non-sintered) state. Layers of metal paste and ceramic paste are joined by a composite paste in green stage. Further gradient porosity can be also introduced in green state with sacrificial spacer which is soluble in non-solvent of the polymer binder.

Functional Gradient formation is by varying the percentage of constituent ceramic and metal or alloy powders from 0% to 100% in the same component or machinable blanks. It is a simple and quick processing route for metals, alloys, ceramics and/or their composites by mixing constituent powder blends in the same binder solution. It can form Solid, Porous or Gradient Porosity in the machinable green body. Porosity can be varied by adjusting the space former size and quantity. Viscosity can be varied for applications ranging from extrusion of blanks to extrusion 3D printing. The resultant functional gradient materials have improved and tailorable physical properties like strength, modulus, fracture toughness and tribology due to combination of different materials and variable porosity. Reactive metals, alloys and ceramic powders can be used due to inert, non-aqueous polymer binder system. Homogeneous green mixtures of the present invention have enhanced shelf life of mixture up to a few months, controlled working time and setting time with specific environmental conditions. Variable yield strength of the mixture is targeted for specific applications ranging from 3D-printing and molding to machinable green blanks by compacting. Reduced wastage due to reusability of the excess or machined debris. The viscosity of the green paste can be adjusted for extrusion based 3D printing. Green mixtures with enhanced shelf life of mixture up to a few months, controlled working time and setting time with specific environmental conditions.

The present invention relates to a green body composition for use in fabrication of a functional gradient material comprising:

(i) Metals, alloys, ceramic powders or a composite thereof ranging from 92 wt% to 97 wt%;

(ii) A non-aqueous thermoplastic binder polymer ranging from 1-6 wt%;

(iii) A solvent ranging from 3-6%;

(iv) A non-solvent ranging from 3-10%; Wherein the thermoplastic polymer has a loading concentration of 1 gm/1.5 ml or 1 gm/2 ml of solvent;

Wherein the solvent to non-solvent is present at a ratio of 0.20 to 1.0.

In an embodiment, metals and alloys are selected from Ti6A14V, steel, Ni, Al, Fe, Ag, Au, Cr, Ta, W, and the like.

In an embodiment, ceramic is selected from alumina, zirconia, hydroxy apatite, bioglass, SiC, AIN, Mullite, Carbon, and the like.

In an embodiment, the thermoplastic binder polymer is selected from poly ethenyl ethanoate, poly vinyl acetate, poly vinyl butyral, epoxy resins and the like. Other polymers are also compatible with the process.

The combination of solvent and non solvent depends on polymer selected. In an embodiment, the solvent is selected from propanol, methanol, ethanol, butanol, acetone, methoxy, propanol or tetra hydro furan. Butanol is a solvent for poly vinyl butyral.

In an embodiment, the non-solvent is selected from hexanol, butanol, pentanol or octanol.

In an embodiment, the composition further comprises viscosity controlling agents ranging from 0.3 to 2wt. %.

In an embodiment, the viscosity controlling agents are selected from stearic acid, citric acid, acetic acid, triglycerides or di butyl phthalate.

In an embodiment, green body is a metal green body, a ceramic green body or a metal-ceramic composite green body.

Further gradient porosity can be also introduced in green state with sacrificial spacer which is soluble in non-solvent of the polymer binder.

In another embodiment, the sacrificial spacer can also be non-soluble in both solvent and non-solvent. In such case they can be removed during binder burnout process at temperatures less than 600°C for ex: polymer beads made of poly styrene, poly styrene sulphonate, polyvinyl acetates, poly vinyl chlorides or open porous poly urethane foam or sponge made of similar polymers can be used. In such cases the porosity of porous body can be increased upto 95 vol %. Further this porous green body can also be attached or layered on a solid green body to make a gradient porous structure which can be subjected to final sintering after spacer and binder bum out process.

In an embodiment, the composition optionally comprises spacer particles selected from salts like NaCl, KC1, and sucrose and the like, having a size ranging from 80 microns to 1000 microns and wherein the spacer is soluble in non-solvent with respect to polymer.

In an embodiment, the green body has a porosity ranging from 10 to 60 Vol % (in porous green body when pore former is introduced. Otherwise solid green body can be made defect free i.e. <0.5Vol% porosity).

In an embodiment, the green body composition is suitable for 3D printing of a metal green body, a ceramic green body or a metal-ceramic composite (cermet) green body.

The present invention also provides a process for preparation of a green body comprising the steps of:

a) Mixing powders of metals, alloys, ceramic or a composite thereof in a thermoplastic polymer solution of solvent and non-solvent; b) Subjected the mixture of step (a) to a high shear mixing for uniform particle distribution to form a green body.

In an embodiment, wherein after step (b) comprises optionally introducing a sacrificial spacer material to obtain a porous green body or coating the green paste or slurry onto an open porous poly urethane foam or sponge. Functional Gradient formation is by varying the percentage of constituent ceramic and metal or alloy powders in the same component or machinable blanks.

In an embodiment of the first method (i.e. functional gradient formation in same component) a method for fabrication of a functional gradient material comprises the steps of: i. Preparing a first layer composed of a metal green body, a second layer composed of a ceramic green body and one or more intermediate layers composed of a metal-ceramic composite green body,

Wherein the relative proportions of metal and ceramic are varied in one direction;

ii. Laminating the first layer, second layer and one or more intermediate layers arranged between the first layer and second layer of step (i) to form a multilayered green structure;

iii. Machining and shaping the multilayered green structure of step (ii) to a near net shape;

iv. Drying the shaped multilayered green structure of step (iii);

v. Sintering the dried multilayered green structure of step (iv) to obtain a functional gradient material;

Wherein the first face of the said material is composed of metal and the second face is composed of ceramic;

Wherein a gradient in concentration ranges across its thickness in a said direction based on the relative proportions of metal and ceramic.

In case of shaping by moulding (according to an embodiment of the present invention) drying comes later. However in another variation of this process, Step iv (drying) may be performed before step iii (machining).

In another embodiment, spacer particles are introduced into the multilayered green structure of step (ii) and wherein the proportion of spacer particles is varied in one direction.

The introduced spacer particles are removed by treating the dried multilayered green structure of step (iv) with the non-solvent and then sintering in step (v) to obtain a functional gradient material having a gradient in porosity, wherein one of the face is porous and the other face is compact, wherein the gradient of porosity ranges across its thickness from highest at one face to lowest at other face.

In an embodiment of the second method (i.e. functional gradient formation by machinable blanks), a method for fabrication of a functional gradient material comprising the steps of: a) Preparing blanks of a solid metal green body, solid ceramic green body, solid metal-ceramic composite green body;

b) Preparing blanks of a porous metal green body, porous ceramic green body, porous metal-ceramic composite green body;

c) Selecting and arranging the prepared blanks of step (a), step (b) or combinations thereof into configurations depending upon the requirement; d) Machining the said blanks of step (c ) to a near net shape;

e) Extruding the shaped blanks, drying and sintering to obtain a functional gradient material.

The functional gradient materials of the present invention can be used for various applications such as biomedical implants.

Dental implants and prosthesis made up of the functional gradient material of the present invention have variable modulus and porous root for bone ingrowth. These dental implants are shaped in the green stage with a simple, cost-effective procedure and novel composition of green body for ceramic, metal, and composite pastes. Also Dental crowns and bridges can be formed by green machining of all ceramic blanks or composite blanks for porcelain fused to composite (PFCom).

Hip or Knee implants and prosthesis where constant relative motion and related wear debris is inevitable, can be improved by joining articular surface made of solid material (e.g. Ceramic) and anchoring surface made of porous part (e.g. porous metallic/composite layer) for bone ingrowth. This can be shaped in green state by using the novel green body composition of the present invention.

Advantages of the present invention are: . A simple green body composition with high concentrated polymer solution and cost effective process of making composite.

• The resulting pastes can be layered into functional gradient components by joining metal paste and ceramic paste into a single unit before sintering.

• The pastes can be molded to near net shapes and dried composite body can be further machined in green state for finer details. • Porosity can be introduced with sacrificial material in to the same pastes and layers. Viscosity of the paste can be adjusted to suite for 3D printing by extrusion nozzles.

• The relative content of rnetal and ceramic powders in composite can be adjusted from 0% to 100% metal or 0% to 100% ceramic.

• Non-aqueous polymer solvent system for reactive metals especially for moisture sensitive materials like titanium and magnesium.

• The fabricated structures may be beneficial for structural, functional as well as biomedical applications.

• Functional gradient implants can reduce stress shielding arising from modulus mismatch

. Dental and orthopedic implants with interconnected macro porous outer shell supports bone ingrowth and even loading of surrounding bone.

. Metal ceramic composites with improved wear resistance compared to metal alone can reduce debris and improve life of implant.

. Ceramic and ceramic matrix composite articular surfaces have beter tribological properties than metals, also the wear debris is relatively inert

• Metal ceramic composites have increased malleability, ductility, fracture toughness and corrosion resistance.

• PFM crowns with metal ceramic composite coping instead of metal coping alone can increase the clinical success rate of these prosthesis due to reduced modulus mismatch.

• Applications in various fields like biomedical implants, defense and aerospace, which involves material processing and shaping of metal ceramic composites, functional gradient materials and gradient porous materials.

• The green body composition of present invention is suitable for 3D-printing.

Applications:

• Biomedical devices, prosthetics and Implants with high load bearing applications and a need to avoid metallic wear particles

• Defense equipment, high strength materials and armor materials • Aerospace and automobile components where high strength to weight ratio at extreme conditions is required

• Components requiring resistance to corrosion, wear and tear along with fracture toughening

· Shaping of Electrical components like resistors and vacuum tube valves, electrode-electrolyte materials and energy storage application.

EXAMPLES:

The following examples are meant to illustrate the present invention. The examples are presented to exemplify the invention and are not to be considered as limiting the scope of the invention

EXAMPLE -1;

Preparation of a green body

Composition for metal paste green composition: 3-6 wt % binder polymer, 1-2 wt% viscosity controlling agents like citric acid, boric acid, acetic acid, triglycerides, etc., 6wt% of solvent like propanol, 8 wt % of non-solvent like butanol or 3 wt% of hexanol. Final set paste after drying has upto 97 wt% of metal, alloy, or their powder blends. To introduce porosity up to 60 vol%, spacer particles of size 80 microns to 1000 microns were added.

Composition for ceramic paste green composition: 3-6wt % binder polymer, 0.3-lwt% viscosity controlling agents like stearic acid, acetic acid, triglycerides, di butyl phthalate, etc., 5wt% of solvent like propanol, 10wt% of non-solvent like hexanol. Final set paste after drying has upto 97 wt% of ceramic or ceramic blend powders. To introduce porosity up to 60vol% spacer particles of size 80 microns to 1000 microns were added. Composition for metal ceramic composite paste green composition: 1-5 wt% of binder polymer, 0.3-lwt% viscosity controlling agents like stearic acid, citric acid, acetic acid, triglycerides, di butyl phthalate, etc., 3-6wt% of solvent like propanol, 5-10% of non- solvent like hexanol or butanol, etc. Final set paste after drying has upto 97 wt% of metal alloy, ceramic or blend powders. To introduce porosity up to 60vol% spacer particles of size 80 microns to 1000 microns were added.

The process for preparation of a metal, ceramic or metal-ceramic composite green body comprises the steps of:

a) Mixing powders of metals, alloys, ceramic or a composite thereof in a thermoplastic polymer solution of solvent and non-solvent;

b) Subjected the mixture of step (a) to a high shear mixing for uniform particle distribution,

c) Shaping the homogenous mixture of step (b) and forming a green body having a near net shape.

The green body can be made porous by introducing a sacrificial spacer material of the appropriate size or by coating onto an open porous poly urethane foam or sponge.

In an embodiment, mixing speed of 10 RPM in high shear mixing, at room temperature for 10-15 minutes is carried out to make solid green mixture. To introduce pores in the as obtained green body, the same mixing conditions with pore former, for 1-2 minutes extra would suffice.

EXAMPLE -2:

Preparation of a functional gradient material

Functional Gradient formation is by varying the percentage of constituent ceramic and metal or alloy powders from 0% to 100% in the same component or machinable blanks.

In method 1 Functional gradient formation in the same component refers to molding the green mixture into near net shape. For e.g. functional gradient implant can be formed by molding coronal 1 /3 ^rd of implant with solid mixture, and after setting time the apical l/3^rd can be molded with porous mixture. (Figure- 22: composite root implant of titanium alloy and alumina)

In method 2 functional gradient formation by machinable blanks refers to layering the different mixtures to form functional gradient blanks and machining the dried set blanks to near net shape (Figure- 2. a, 2.b- functional gradient block made from titanium and alumina joined composite middle layer)

Figure-2 illustrates a photographic image of functional gradient block made from titanium and alumina with composite middle layer (a) after drying and (b) after sintering. The functional gradient block has top layer made of 100%alumina( white) middle layer made of 50% titanium and 50% alumina mixture(light grey) and bottom layer 100% Titanium alloy(dark grey). In this sample all the 3 layers were separately mixed, moulded into separate layers and then adhered together before drying to form a machinable blank.

Figure-3 illustrates a micro CT image of sintered titanium with solid over porous layers. This sample was prepared by mixing titanium alloy powder with 4wt% binder and forming a sheet in the first step. In the second step salt crystals were added to make 60 Volume% porosity in the mixture and mixed for 2 minutes. Then both the layers were joined together before drying. After complete drying and setting the sample was treated with water to remove salt spacer. Then again the samples were dried to remove moisture followed by sintering. Since the polymer binder being used was hydrophobic it would protect the reactive metal powders from oxidation in water.

In some embodiments, composite block of Ti6A14V-Al₂03 were prepared and tested in various configurations. The composite blocks were made with 50 wt% of Ti6A14V and 50 wt% of alumina with ~4 wt% of binder and ~0.5 wt% stearic acid and solvent to non solvent ratio would be 0.2 to O.6., the porous blocks were having -55 Vol % of porosity.

Figure-4 illustrates a photographic image of porous Ti6A14V-Al₂0₃ composite block, Figure -5 illustrates a photographic image of a composite block machined to implant. Figure-6 illustrates photographic image of a porous + solid sandwich composite block Figure-7 illustrates photographic image of a machined Ti6A14V-Al₂C)3 composite

Figure-8 illustrates a micro-CT image of machined Ti6A14V-Al₂03 composite

Figure-9 illustrates (A) (B) (C) SEM images of Ti6A14V-Al₂0₃ composite at 1.5KX, 5KX, 25KX (KX refers to magnification of Scanning electron microscopy image. E.g. 5KX means magnified 5000 times)

Figure-10 illustrates extruded porous and solid green T16AI4V-AI₂O₃ composite.

Figure-11 illustrates extrusion graph of porous CERMET dough. This graph represents stress-strain curve of the composite mixture with pore formers during extrusion into green cylinders. The smoothness of the graph in the plateau region from 0.4-0.5 MPa stress represents the uniform mixture. Also the low yield strength of the mixture i.e. 0.41 MPa in the graph represents that the mixture can be deformed in to shapes with minimal force.

Figure-12 illustrates XRD of T16AI4V-AI₂O3 composite.

In some other embodiments, green ceramic blocks have been synthesized at various configurations ceramic blocks were extruded from green body of alumina and poly vinyl acetate binder using isopropanol-hexanol solvent and nonsolvent mixture in high shear mixing. The binder is ~4 wt% and viscosity controlling agents like stearic acid is ~2 wt % in the composition. Solvent to non solvent ratio would be 0.2-1. These blanks were vacuum dried and machined into dental crowns, bridges and implants before sintering.

Figure-13 illustrates a photographic image of porous + solid sandwich ceramic blocks

Figure-14 illustrates a micro CT image of sandwich porous and solid ceramic

Figure-15 illustrates a micro CT image of extruded porous ceramic.

Figure-16 illustrates a ceramic block machined to dental bridge.

Figure-17 illustrates a green ceramic molar crown CNC machining.

In some embodiments, green metal/alloy blocks/sheets have been synthesized at various configurations:

Figure-18 illustrates photographic image of a green molded titanium sheet Figure-19 illustrates photographic image of a titanium sheet for machining

Figure-20 illustrates a green magnesium block for machining.

EXAMPLE -3:

Dental implant with functional gradient design and variable elastic modulus:

Ex 1 : In dental implants the core of the implant can be formed by composite with at least

40 wt % of ceramic to introduce high modulus core. This core extends coronally, forming an abutment in case of single piece implant or an attachment for abutment in case of two- piece implant. This abutment supports the ceramic crown which has higher or similar modulus than the abutment. The outer shell of the implant can be made of at least 60 wt% of metal or can be 100 % metal. In this outer shell porosity can be introduced in all of the root part, or only in middle 3rd, or only apical 3rd of the root part.

Ex 2: The dental implant can also be made of 100 % metal or 100% ceramic or 100% composite as per the requirement, where the inner core is solid and outer shell is porous and these layers can be laminated and machined in green stage and then sintered. The resulting implants can be only ceramic or metal or composite with outer porous part and inner solid part.

Ex3: PFM crowns and bridges, where metal coping is replaced by metal ceramic composite, made by green state machining of composite blank. This reduces modulus mismatch between porcelain and metal layers

Ex4: further in case of porous implants for bone ingrowth, in the sintered component the porosity can be filled with another green paste made from bioglass powder and sintered again. After implantation the bioglass resorbs gradually into the body and stimulates bone formation in the porosity left behind by bioglass.

Ex5: For composite implant where the ceramic portion is bioresorbable in nature like calcium phosphate Apatite, the porosity left behind by the resorbed ceramic portion would act as porous part and facilitate bone ingrowth.

Figure-21 illustrates various configurations (a, b, c, d, and e) of a dental implant with functional gradient design and variable elastic modulus. The dental implant (100) comprises a crown (101) and root implant (102) connected by an abutment. The crown (101) is composed of a ceramic body. The root implant has an inner core (103) and, an outer shell (104) surrounding the solid inner core (103).

The crown (101) is composed of a solid ceramic body (1). The inner core (103) is composed of a solid metal body (3), solid ceramic body (1) or a solid metal-ceramic composite body (5). The apical portion of the outer shell (104) is composed of a porous metal body (4), porous ceramic body (2) or a porous metal-ceramic composite body (6).

Elastic modulus (300) of solid ceramic>solid metal-ceramic composite>solid metal> porous metal.

Thus the dental implants formed from the functional gradient material of present invention have a variable elastic modulus and gradient in density, porosity.

Figure-22 illustrates a composite root implant of titanium alloy and alumina, as sintered a) micro-CT image b) photographic image. Example of metal ceramic composite dental implant with porous root part for bone ingrowth. The sample is made by green shaping with the above mentioned process and composition. It shows coronal portion with abutment fixture (10), a middle l/3^rd with solid core and porous outer surface (11) and an apical 1/3^rd with porous part (12). The sample needs final trimming and finishing however the Micro CT of sample shows very good interfacial bonding at the porous and solid junction.

EXAMPLE -4: Hip and knee implant

Hip or knee implants can be made by green near net shaping, with ceramic, or metal ceramic composite solid layers forming the articular ends to reduce frictional wear and tear, while the other end in contact with the bone can be made porous with metal, ceramic, or a composite mixture to facilitate bone ingrowth and osseointegration.

Figure 23 illustrates a hip implant composed of a functional gradient material according to present invention.

The functional gradient hip implant (200) comprises (i) An acetabular cup (201) adapted to receive a femoral head (205), wherein the said acetabular cup comprises an outer acetabular shell (202), a transition layer (203) and an acetabular cup liner (204);

(ii) A femoral head (205) and ;

(iii) A femoral stem (206) attached to the femoral head (205);

Wherein the hip implant comprises a functional gradient material prepared from a green body by the method of present invention;

Wherein the outer acetabular shell (202) is made of a porous metal layer

(1), the transition layer (203) is composed of a metal-ceramic composite

(2) and the acetabular cup liner (204) is composed of a ceramic layer (3); Wherein the femoral head (205) is composed of a ceramic layer (3);

Wherein the femoral stem (206) is attached to the femoral head (205) by a metal-ceramic composite layer (2);

Wherein the femoral stem (206) is composed of an inner solid metal layer (4) surrounded by an outer porous metal layer (1)

Hip implant with porous metal for bone ingrowth and solid ceramic articular surfaces reduces wear and tear and composite layer in between metal and ceramic layers.

EXAMPLE -5:

Characterization of functional gradient material:

Functional gradient material prepared according to the present invention has improved and tailorable physical properties like strength, modulus, fracture toughness and tribology due to combination of different materials and variable porosity. Green mixtures of the present invention have enhanced shelf life of mixture up to a few months, controlled working time and setting time with specific environmental conditions. It has been observed from experiments the green ceramic mixture formed, retained its consistency and shape formability in an air tight or sealed container for more than 8 weeks.

The concept of functional gradient materials and metal ceramic composite materials having improved physical properties is well documented in the literature. But the novelty of the present invention is a green composition and efficient method of shape forming of these materials. Figure-24 illustrates a SEM image which shows different layers in functional gradient block (a) Ti6A14V (b) Alumina (c) Ti6A14V+Alumina composite

The thermoplastic polymer is at a higher loading concentration of solvent and the solvent-nonsolvent combination is present at a particular ratio in the novel green body composition of the present invention. A higher loading polymer concentration refers to dissolving the polymer in optimal solvent to non-solvent ratio.

Figure-25 illustrates a mixture with varying solvent to non-solvent ratio.

(a) Alumina mixture with solvent to non-solvent ratio >1.0

(b) Alumina mixture with optimized ratio 0.2 to 0.6

(c) Bar extruded from optimized mixture

(d) Bar extruded from alumina mixture with solvent to non-solvent ratio <0.2 showing surface defects

It is observed that the ratio of solvent to non solvent in the present composition could be varied successfully from 0.20 to 1.0 depending on the required viscosity, powder blend combination and intended application. Within this range the polymer would just dissolve in the solvent in a higher concentration, but will be distributed freely in the non solvent phase thereby coating the particles evenly forming a uniform moldable mixture Figure-25 (b), (c). If the ratio is less than 0.20 the mixture will have non-homogeneous polymer distribution, where the polymer does not dissolve completely forming clumps in the mixture there by forming defects which reduce the green strength and uniformity Figure-25 (d). In contrast if the ratio is more than 1.0 the particles settle down from the mixture and the dissolved polymer separates out from the settled powder clumps resulting in a mixture which is unstable Figure-25(a). This is evident from Figure-25 where (a) shows unstable mixture, (b), (c) shows a workable and shape formable mixture and extruded bar, (d) shows a bar extruded from mixture with surface defect.

Figure-26 illustrates (a) Porous alumina sponge with ~95 vol % porosity after sintering (b) Green porous titanium sponge. The green mixture of (a) pure alumina (b) pure Ti6A14V was coated on the struts poly urethane sponge. The viscosity of the mixture was decreased by increasing the solvent to non-solvent ratio from 0.6 to 1. This made the mixture thin enough to be coated on to the struts.

3D-printing

Figure-28 illustrates Extrusion 3D printed (a) CERMET (b) Pure Alumina after printing (c) Pure Alumina after sintering

It is to be understood that the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention.

Claims

1. A green body composition for use in fabrication of a functional gradient material comprising:

(i) Metals, alloys, ceramic powders or a composite thereof ranging from 92 to 97 wt%;

(ii) A non-aqueous thermoplastic binder polymer ranging from 1-6 wt%;

(iii) A solvent ranging from 3-6%;

(iv) A non-solvent ranging from 3-10%;

Wherein the thermoplastic polymer has a loading concentration of 1 gm/1.5 ml or 1 gm/2 ml of solvent;

Wherein the solvent to non-solvent is present at a ratio of 0.2 to

1 0

2. The green body composition according to claim 1 , wherein the metals and alloys are selected from Ti6A14V, steel, Ni, Al, Fe, Ag, Au, Cr, Ta, W, and the like.

3. The green body composition according to claim 1, wherein the ceramic is selected from alumina, zirconia, hydroxy apatite, bioglass, SiC, AIN, Mullite, Carbon and the like.

4. The green body composition according to claim 1, wherein the thermoplastic binder polymer is selected from of poly ethenyl ethanoate, poly vinyl acetate, poly vinyl butyral, epoxy resins and the like.

5. The green body composition according to claim 1, wherein the solvent is selected from propanol, methanol, ethanol, butanol, acetone, methoxy propanol or tetra hydro furan.

6. The green body composition according to claim 1, wherein the non-solvent is selected from hexanol, butanol, Pentanol or Octanol.

7. The green body composition according to claim 1 wherein, the composition further comprises viscosity controlling agents ranging from 0.3 to 2 wt.%.

8. The green body composition according to claim 7, wherein the viscosity controlling agents are selected from stearic acid, citric acid, acetic acid, triglycerides or di butyl phthalate.

9. The green body composition according to claim 1, wherein the said green body is a metal green body, a ceramic green body or a metal-ceramic composite (cermet) green body.

10. The green body composition according to claim 1, wherein the composition optionally comprises spacer particles selected from salts like NaCl, KC1 and Sucrose and the like, having a size ranging from 80 microns to 1000 microns; wherein the salt spacer is soluble in non-solvent and wherein the said composition has a porosity ranging from 10 to 60 vol%.

11. The green body composition according to claim 1, wherein the composition optionally comprises spacer particles selected from polymer microbeads from materials like poly styrene, poly styrene sulphonate, polyvinyl acetates, poly vinyl chlorides open porous poly urethane foam or sponge made of similar polymers; wherein the said polymer spacer is non-soluble in both solvent and non-solvent and wherein the green paste or slurry is coated on to the said open porous foam or sponge struts to obtain 95 Vol % of porosity.

12. The green body composition according to any one of the preceding claims, wherein the said composition is suitable for 3D printing of a metal green body, a ceramic green body or a metal-ceramic composite (cermet) green body.

13. A process for preparation of a green body according to any one of the claims 1-12 comprising the steps of:

b) Subjecting the mixture of step (a) to a high shear mixing for uniform particle distribution to form a green body that can be shaped to a near net shape.

14. The process according to claim 13, wherein the green body is a metal green body, a ceramic green body or a metal-ceramic composite (cermet) green body.

15. The process according to claims 13-14, wherein the green body obtained in step (b) is further subjected to drying and sintering to form a solid metal green body, a solid ceramic green body or a solid metal-ceramic composite (cermet) green body.

16. The process according to claim 13, wherein after step (b) comprises optionally introducing a sacrificial spacer material according to claim 10 or coating the green paste or slurry onto an open porous poly urethane foam or sponge according to claim 11 to obtain a porous green body that can be shaped to a near net shape.

17. The process according to claim 16, wherein the porous green body is a porous metal green body, a porous ceramic green body or a porous metal-ceramic composite green body.

18. The process according to claims 16-17, wherein the introduced salt spacer particles which are soluble in non-solvent are removed by treating with the non solvent or wherein the coated polymer spacer particles which are non-soluble in both solvent and non-solvent are removed by heat treatment at a temperature less than 600°C and then subjected to drying and sintering to form a porous metal body, a porous ceramic body or a porous metal-ceramic composite (cermet) body.

19. A method for fabrication of a functional gradient material comprising the steps of: i. Preparing a first layer composed of a metal green body, a second layer composed of a ceramic green body and one or more intermediate layers composed of a metal-ceramic composite green body,

iv. Drying the shaped multilayered green structure of step (iii);

Wherein the first face of the said material is composed of metal and the second face is composed of ceramic; Wherein a gradient in concentration ranges across its thickness in a said direction based on the relative proportions of metal and ceramic.

20. The method according to claim 19, wherein spacer particles are introduced into the multilayered green structure of step (ii) and wherein the proportion of spacer particles are varied in one direction.

21. The method according to claim 20, wherein the introduced spacer particles are removed by treating the dried multilayered green structure of step (iv) with the non-solvent and then sintering in step (v) to obtain a functional gradient material having a gradient in porosity, wherein one of the face is porous and the other face is compact, wherein the gradient of porosity ranges across its thickness from highest at one face to lowest at other face.

22. A method for fabrication of a functional gradient material comprising the steps of: a) Preparing blanks of a metal green body, ceramic green body, metal- ceramic composite green body;

c) Selecting and layering the prepared blanks of step (a), step (b) or combinations thereof into configurations depending upon the requirement; d) Machining the said blank configurations of step (c) to a near net shape; e) Extruding the shaped blanks, drying and sintering to obtain a functional gradient material.

23. A functional gradient material prepared by a method according to any one of the claims 19-22.

24. A dental implant comprising the functional gradient material according to claim 23.

25. An orthopaedic implant or prosthesis comprising the functional gradient material according to claim 23.

26. A functional gradient dental implant (100) comprising:

(i) a crown (101); and

(ii) root implant (102) connected by an abutment; Wherein the said dental implant is composed of a functional gradient material having a variable elastic modulus prepared from a green body having a near net shape by a method according to claim 22;

Wherein the crown (101) is made of a solid ceramic body (1); Wherein the root implant (102) comprises an inner solid core (103) selected from a solid metal body (3), solid ceramic body (1) or a solid metal-ceramic composite body (5) and,

an outer shell (104) surrounding the solid inner core wherein the apical portion of the said shell (104) is made up of a porous metal body (4), porous ceramic body (2) or a porous metal-ceramic composite body (6);

Wherein the elastic modulus of solid ceramic>solid metal-ceramic composite>solid metal> porous metal.

27. A functional gradient hip implant (200) comprising:

(i) An acetabular cup (201) adapted to receive a femoral head(205), wherein the said acetabular cup comprises an outer acetabular shell (202), a transition layer (203) and an acetabular cup liner (204);

(ii) A femoral head (205) and ;

(iii) A femoral stem (206) attached to the femoral head (205);

Wherein the said hip implant is composed of a functional gradient material prepared from a green body having a near net shape by the method according to any one of claims 19-21;

Wherein the outer acetabular shell (202) is made of a porous metal layer

(1), the transition layer (203) is composed of a metal-ceramic composite