JP2572777B2 - TiC particle dispersion strengthened titanium base alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention further provides abrasion resistance and heat resistance to Ti or a Ti alloy having characteristics such as light weight, high strength, and high corrosion resistance. Ti that can be applied as a material
It relates to a C particle dispersion strengthened titanium-based alloy.

[Prior art] Conventionally, steel materials such as bearing steel (SUJ-2) have been widely used as metal materials requiring abrasion resistance. Speed steel, cemented carbide, cermet, etc. are used,
Recently, the use of ceramics has been studied. However, each of these wear-resistant materials has the following disadvantages.

That is, since steel material has a large specific gravity, when it is used as a wear-resistant part that rotates or reciprocates, there is a problem that a heavy load is imposed on a movement mechanism and energy loss increases. For example, engine parts (intake valve, valve locker) , Connecting rods, valve retainers, rocker arms, etc.) increase fuel efficiency. Further, since the high-speed steel and the cemented carbide have a higher specific gravity, the above-mentioned disadvantages are further emphasized. Ceramics, on the other hand, are lightweight and do not suffer from the above-mentioned problems encountered with steel materials, but are not only complicated in production, but also have extremely low ductility and toughness, so they have poor reliability against impact fracture and other problems. It is hard to say that it satisfies the overall quality as a part.

Various particle-dispersed alloys have been developed and attracted attention as new wear-resistant materials for solving such disadvantages. That is, a particle-dispersed alloy is a composite of a compound such as carbide, boride, silicide, nitride, or oxide having high heat and wear resistance and a high toughness metal. Powder metallurgy is the most common method of mixing and sintering after press molding, and other methods such as melt mixing, internal oxidation,
A surface oxidation method and the like are known.

[Problems to be Solved by the Invention] However, the above-mentioned particle-dispersed alloys have the following disadvantages, including the production method thereof.

Uniform mixing of the dispersed particles and matrix metal is difficult,
There is a problem with homogeneity.

Unless the sintering or hot extrusion and the compounding step are combined, the strengthening effect by the dispersed particles is hardly obtained, and the productivity is low.

The dispersed particles and matrix are often in a thermodynamically unstable state in the coexistence state, and the dispersed particles (compound) and matrix (metal) are thermodynamically stable during the heat treatment in the subsequent process or when used under high temperature conditions. In some directions (solid solution, recrystallization, diffusion, transformation, etc.), and the composite material itself is liable to be deteriorated.

On the other hand, titanium and titanium alloys have features such as light weight, excellent corrosion resistance and high strength,
Although it is used as a structural material for a flying object such as an aircraft, it cannot be applied to a sliding portion that receives friction as it is because of its poor wear resistance. Therefore, when applied to a portion subject to friction, a method of performing a surface hardening treatment such as nitriding, thermal spraying or the like is employed. However, these surface hardening methods cannot provide satisfactory wear resistance.

The present invention has been made in view of such circumstances, and its purpose is to maintain the light weight, high corrosion resistance, and high strength of titanium and titanium alloys, and have the disadvantages of abrasion resistance and heat resistance. Properties are improved by compounding with dispersed particles without causing the problems pointed out for the particle-dispersed alloys, and lightness, corrosion resistance, strength, heat resistance, and abrasion resistance can be satisfied. It is intended to provide materials.

[Means for Solving the Problems] The constitution of the particle-dispersion-strengthened titanium-based alloy according to the present invention, which can achieve the above object, is 1.8 to 18% by weight of C.
Containing TiC in a titanium or titanium alloy matrix
The gist is that the particles are uniformly dispersed and crystallized.

[Action] The disadvantage of the conventional particle-dispersed metal or alloy is that, as described above, the dispersed particles (compound) and the matrix coexist and are thermodynamically unstable. When used below, the compound or matrix changes in a thermodynamically stable direction, and the properties as a composite material change. Therefore, in order to remedy such a drawback, it is necessary to maintain a stable state, that is, a thermodynamic equilibrium state of a matrix and a compound made of a metal or an alloy in a coexisting state. One idea for this purpose is, for example, a composition in which a liquid phase and a compound (carbide, nitride, oxide, intermetallic compound) can coexist in an equilibrium phase diagram of an alloy. A method in which the melt is cooled to a solid after heating and holding at a temperature in the range described below is considered. That is, in the process of cooling and solidifying the molten mixture, when the liquid phase in the coexistence region of the liquid phase and the compound solid phase solidifies to a solid phase, transformation occurs at this time, and a solid single phase of the alloy or a compound ( This compound may be different from the compound that coexisted with the liquid phase), but in any case, this solid phase becomes a particle-dispersed alloy in which the compound is dispersed in an alloy matrix. If the content as a compound is properly adjusted, a composition similar to that of a conventional particle-dispersed alloy should be obtained. Moreover, if this method is adopted, the solid phase gradually crystallizes out of the liquid phase and eventually the whole solidifies, so that the matrix and the crystallized particles (compound) are in a thermodynamically stable state, It is considered that transformation at the interface is unlikely to occur.

On the other hand, as a measure for improving the insufficient wear resistance of titanium and titanium alloy, dispersion strengthening of hard particulate matter can be considered.
This is derived from the mechanism of improvement in wear resistance of steel materials. Steel has a composite structure in which hard carbides (cementite and alloy carbides) are dispersed in a matrix (ferrite or martensite). The wear properties are significantly increased.

Therefore, it is considered that the wear resistance of titanium and titanium alloys can be significantly improved if a composite structure in which ultra-hard carbide particles are dispersed in a matrix can be formed as in the case of wear-resistant steel. In this case, if the coexisting carbide and titanium or titanium alloy are in a composite structure in a thermodynamic equilibrium state, problems such as transformation caused by the thermodynamic instability seen in the particle-dispersed composite alloy as described above. Should not happen.

From this viewpoint, a study based on a binary alloy equilibrium diagram made of Ti-C shows that a hard carbide that can stably coexist thermodynamically is TiC, and that the dispersion of the TiC particles improves the wear resistance. Is exerted not only in a titanium matrix but also in a coexistence system with a matrix composed of an α alloy, an α + β alloy or a β alloy containing various alloying elements together with titanium.

Considering the case where TiC is crystallized based on a TiC equilibrium diagram from a liquid phase coexistence system in which a wt% of carbon is added to pure titanium, all of the added carbon reacts with titanium to form TiC.
Occupy in solidified composite tissue
The volume fraction (V _f ) of TiC can be represented by the following approximate expression.

This relationship is illustrated in FIG. 1 and shows that the TiC volume ratio (V _f ) has a linear relationship with the amount of carbon added, and that the volume ratio of TiC can be arbitrarily adjusted by the amount of carbon added. . This tendency is basically the same even when carbon is added to various titanium alloys to generate TiC.

When TiC is generated and dispersed in the titanium or titanium alloy matrix in this manner, the TiC becomes extremely hard ( _Hv : 3000
Degree) Since the particles are particles, the entire composite material is remarkably hardened by the compounding rule and has excellent wear resistance. However, according to the experiments, if the volume ratio of TiC is less than about 10%, the absolute amount of hard particles is insufficient, so that a satisfactory effect of improving wear resistance cannot be obtained. The toughness of the material becomes poor, and cracks and other defects tend to occur. From such a point, the addition amount of carbon should be adjusted so that the volume ratio of TiC becomes about 10 to 90%. From the relationship between the volume ratio of TiC and the carbon amount shown in FIG. The range of 1.8 to 18% by weight of the amount of carbon required to secure the wear resistance is derived.

[Example] Example 1 C: A 200-g ingot (width 40 x length 80 x thickness 15 mm) containing 0 to 18.5% by weight and the balance consisting of Ti and inevitable impurities was melted by a tungsten arc melting method. Using this ingot, (I) as it is, and (II) after being heated to 1150 ° C, subjected to 50% hot rolling and further annealed at 750 ° C,
Measurement of TiC volume ratio by optical microscope (using image analyzer), Vickers hardness measurement and wear test using SUS304 as a mating material (300m distance using Ogoshi type abrasion tester)
(Evaluated by the amount of abrasion per unit area when moved).

The results are as shown in Table 1. As the amount of added carbon increases, the volume ratio of TiC increases almost proportionally, and accordingly, the hardness of the composite material increases and the wear resistance improves. However, when the carbon content exceeds 18% by weight, the TiC volume ratio exceeds 90%, and the impact strength is adversely affected.

Example 2 Several kinds of titanium alloy ingots having different carbon contents were produced in the same manner as in Example 1 except that Ti-6A1-4V alloy was used in place of pure titanium, and as-cast materials and hot-rolled and annealed materials A similar test was performed for

The results are as shown in Table 2, which shows almost the same tendency as the experimental results for pure titanium shown in Table 1. FIG. 2 shows Ti-6A1-4V to which 6% by weight of carbon was added.
It is an optical microscope photograph instead of a drawing showing the metallographic structure of the alloy (as-cast material), and it can be seen that it has a composite structure in which granular TiC is uniformly dispersed.

[Effects of the Invention] The present invention is configured as described above, and its effects are summarized as follows.

(1) Abrasion resistance can be significantly enhanced while maintaining the lightweight, high corrosion resistance, and high strength characteristics of titanium or titanium alloy, and it is advantageously used as a rotating or reciprocating member that is lightweight and does not impose a burden on the movement mechanism. can do.

(2) TiC particles for improving abrasion resistance are crystallized in a matrix by bonding to carbon contained in molten titanium or a titanium alloy, and TiC and the matrix coexist in a thermodynamic state. Therefore, there is no danger of causing a solid solution, re-precipitation, diffusion, transformation, etc., when used at a high temperature as in a conventional particle-dispersed alloy, to cause a deterioration.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of carbon added in titanium and the volume fraction of TiC, and FIG. 2 is an optical microscope photograph showing the metal structure of the TiC particle dispersion strengthened titanium-based alloy according to the present invention.

Continuation of the front page (56) References JP-A-62-222041 (JP, A) JP-B-46-17044 (JP, B1) JP-B-54-19846 (JP, B2)

Claims (1)

(57) [Claims] 1. A TiC particle dispersion strengthened titanium base alloy containing 1.8 to 18% by weight of C, wherein TiC particles are uniformly dispersed and crystallized in a titanium or titanium alloy matrix.