JPH02232303A - Manufacture of titanium alloy powder sintered product - Google Patents

Abstract

PURPOSE:To save machining and grinding stages and to obtain a sound product at high efficiency by pressurizing sintered Ti alloy in the specific temp. range and removing the residual voids on the surface layer with shot peening. CONSTITUTION:The Ti alloy constituting metal element powder is mixed, and compacting and vacuum-sintering are executed to executed HIP treatment. Then, the sintered Ti alloy is pressurized in the alpha+beta two phase range at temp. from 700 deg.C to beta transformation temp. to suppress the residual voids. The shot peening is executed to the surface of the HIP semiproduct to remove the residual voids on the surface layer. By this method, the Ti alloy sintered product having little residual voids can be manufactured at good yield and a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a titanium alloy powder sintered product, which improves the yield and reduces the cost of the powder sintered titanium alloy product. [Prior Art] Titanium and titanium alloys have high specific strength, and are materials with excellent toughness, corrosion resistance, heat resistance, etc., but titanium alloys have some drawbacks in terms of melting, forging, machinability, etc. For this purpose, various so-called near net shape processing techniques have been attempted, and one of the leading techniques is a powder metallurgy method. The powder metallurgy method for titanium alloys uses powders with predetermined alloy components as raw material powders, and processes the sintered titanium alloys through powder compacting (hereinafter referred to as CIP) and vacuum sintering using high-temperature isostatic pressure. A typical method is a raw powder mixing method (hereinafter referred to as old P) in which the powder is pressed down and molded.

It has been revealed that titanium alloys produced by such a raw powder mixing method exhibit tensile properties, fracture toughness, and fatigue properties that are almost equivalent to those produced by the ingot melting and rolling method. In addition, using powder as a starting material has the advantage that a wide variety of products can be easily molded into the final product shape (net shape) or a shape close to the final product (near net shape), and the market will continue to expand in the future. We can expect that.

Here, as a product development need, there is a desire to supply small-lot products that utilize the functionality of titanium and titanium alloys, and there is an increasing demand for products with even lower prices. However, with the above method, microporosities (residual voids) remain on the surface, and cutting and surface machining processes are essential in the process of turning the material into a product, which requires a large amount of cost and is also time consuming. The reality is that it will inevitably become longer and it is impossible to reduce the price.

[Problems to be Solved by the Invention] The present invention provides a highly efficient manufacturing method that further simplifies the above-mentioned manufacturing process.

It is a powder metallurgy process that has the advantage of being easily molded into the final product shape or a shape close to the final product.
Even after the P treatment, a large number of particles are observed on the surface layer of the sintered product. If these microporosities exist in the final product, they become the starting point for fatigue cracks and deteriorate fatigue properties. On the other hand, it has been said that shot peening significantly improves the fatigue life of mechanical parts. It has been well known that this effect significantly improves the fatigue properties of spring materials and wire rods {for example, Metal Handbook, Revised 4th Edition (Maruzen).
1982) P812} is not widely used in powder sintered products, except for some parts. Powder sintering technology has made great progress in recent years. Although NearNetShape technology has significantly developed, the surface finish of products is still machine-ground, and efforts are being made to extend the fatigue life of mechanical parts by applying shot peening to the machine-ground finished surface. Mechanical grinding to remove voids remaining in the surface layer of powder sintered semi-finished products not only increases product manufacturing costs but is also a major factor in reducing product yield. In particular, there is an increasing need for the use of titanium and titanium alloy materials as functional materials, and there are many demands to reduce their manufacturing costs. Therefore, it has become necessary to further simplify the manufacturing process and improve its functional characteristics. Therefore, the present inventors combined the selection of the mold material, the powder sintering process, and the shot peening surface finishing process to obtain the desired material dimensions and surface condition, thereby shortening the product manufacturing process, improving yield, and reducing costs. We invented a method for manufacturing titanium alloy powder sintered products. First, we investigated ways to reduce the weight of connecting rods for engine parts, and developed a manufacturing technology for powder-sintered titanium alloy products that would reduce costs. In particular, the following three points were devised to fully utilize the surface modification effect of shot peening. 1) Improvement of fatigue properties: Generation of residual compressive stress by shot peening and its utilization. 2) Detoxification of residual voids in the product surface layer - Collapse of microporosity existing in the surface layer, acceleration of work hardening in the vicinity, and peeling of the hardened layer. 3) Beautifying the surface of IT products: ensuring an appearance and gloss comparable to mechanical grinding. The present invention was completed based on these basic findings. [Means and effects for solving the problem] The focus of the present invention is on the manufacturing technology and shot peening technology of titanium alloy powder sintered products using the alloy powder method and the raw powder mixing method, which the present inventor has researched for many years. It is in. That is,
Instead of the conventional melting method, a mixed powder that has been mechanically mixed in advance to have a specified alloy component is compacted into a specified shape using a die press, cold isostatic press, etc. to form a CIP product. This project utilizes the large number of residual voids found in the surface layer of sintered titanium alloy HIP products manufactured through the vacuum sintering process to simplify the manufacturing process. In the conventional method, the voids remaining in the surface layer of powder sintered products were removed by mechanical grinding. In the present invention, the residual voids are crushed by shot peening, the surface layer is work-hardened from the surface in the depth direction, and residual compressive stress is generated by shot peening, and the interface part of the crushed residual voids is crushed to the surface during shot peening. The work-hardened surface area is used as the starting point for layer peeling, and the surface is finished to be equivalent to mechanical grinding. In other words, when producing a titanium alloy powder sintered product, the sintered titanium alloy produced through the processes of mixing the constituent metal element powders, compacting, and vacuum sintering is heated in the α + β two phase region at a temperature of 700°C or higher up to the β transformation point temperature. We have established a method for producing powder sintered products of titanium and titanium alloys, which is characterized by applying pressure and removing the remaining voids in the surface layer of semi-finished products by shot peening to finish the surface. The present invention will be explained in detail below. In the present invention, titanium alloys include Ti, for example, A Q , V, Mo, Cr, Zr. S
It can be applied to titanium alloys containing one or more of n, Fa, etc.

The transformation point of the sintered product is determined by differential thermal analysis. Mix the constituent metal element powders of titanium alloy. II is a sintered titanium alloy manufactured through a vacuum sintering process after compacting into the final product shape or a shape close to the final product.
Perform IP processing. If you cut a HIP-treated semi-finished product that has been sintered after CIP and observe the cross section IIim, the residual voids may exist deep inside the product. This means that the product usage characteristics standards are not met. Semi-finished products that have been sintered after CIP are subjected to }IIP
When processed, hydrostatic pressure and specific temperature conditions result in a collection of residual voids in the surface layer of the HIP product. They are often found at a depth of about 200 μm below the surface.If the depth exceeds this, the effect of the present invention will be reduced, so the depth at which residual voids exist is set at 150 μm. .

The shallower the depth, the smaller the amount of peeling due to shot peening, and the higher the yield. The depth at which these residual voids exist depends on the heating temperature and pressure of HIP. 700℃
By applying pressure in the α+β two-phase region up to the β transformation temperature, residual voids can be suppressed to a depth of about 150 μm. At the IIP heating temperature of less than 700℃, approximately 200℃ below the surface.
Residual voids larger than μm become visible and fatigue properties, tensile properties, etc. deteriorate. Furthermore, heating above the β-transformation point causes the structure to coarsen, resulting in poor fatigue properties and tensile properties.
Although the pressing force is not specified, under the heating temperature conditions limited here, good results can be obtained under isostatic pressing conditions using a pressure of 250 kg/cm2 or more for 1 hour or more. Furthermore, the higher the applied pressure, the shallower the depth of residual voids. The voids remaining in the surface layer of the IIIP semi-finished product are crushed by shot peening, and the work-hardened layer is peeled off and removed to finish the surface. In sheet beaning, which involves projecting steel balls, the size, hardness, and projecting speed of the steel balls affect the collapse of residual voids. These conditions are selected depending on the composition of the titanium alloy. The standard measures the hardness of titanium alloy, and when a spherical object with a harder hardness is projected at a speed of 10 m/see or higher, the remaining voids are crushed and peeled off within 20 to 40 minutes, resulting in a beautiful metallic luster. It will be done. Although the size of the steel ball is not limited, the purpose can be achieved by projecting with a steel ball having a diameter of 100μ to 600μ, which is larger than the surface roughness of the sintered product and the lIPi2 product.

[Example] (1) Two types of powder, that is, the composition is titanium 99
．． We prepared sponge titanium powder consisting of 6% titanium powder and additive master alloy powder whose composition was 60% aluminum and 40% vanadium. (2) First step: Titanium powder and additive master alloy powder were mechanically mixed at a weight ratio of 9:1. Second step: The mixed powder was inserted and filled into a predetermined elastic mold.
CIP test pieces were prepared so that the product would be a fatigue and tensile test piece with a diameter of 10+++ m after HIP. Third step: The filled powder was compacted using a hydrostatic press. Fourth
Process: Press the compact into a vacuum of 10-'torr, 1250℃
It was sintered. 5th step = 1000kg/cm”,
Hot isostatic pressing was performed at 900°C for 3 hours.
6th step: In order to compare the shot peening process with and without shot peening, the shot peening conditions were set to 0.
6yata diameter steel ball (hardness} lv590) at 48m/s
Projected with ec. There were two levels: 20 minutes and 40 minutes. Machine-ground materials were also used for comparison. The β transformation point of this alloy is 9
The temperature is 90℃. (3) Figures 1, 2, and 3 show the surface characteristics of the metal structures of Ti-6A Q-4V alloys produced by the conventional method (without shot peening) and the method of the present invention. As is clear from Figure 2, the residual voids in the alloy produced by the method of the present invention are collapsed. Furthermore, FIG. 3 shows the surface area of the work-hardened layer near the crushed residual void in FIG. 2, separated by flI1. Tensile test specimens and fatigue test specimens were made from this alloy and tested on each. Fatigue test conditions are axial load, R = -1.0
, f=20Hz, in the atmosphere, at room temperature. The tensile test results are shown in Table 1, and the fatigue properties are shown in Figure 4. As shown by the results, the alloys according to the mechanical properties shown in Table 1 obtained by the method of the present invention had properties equivalent to those obtained by mechanical grinding compared to the conventional method.

[Effects of the Invention] A feature of the present invention is that even for sintered products with complex shapes, by devising the projection angle etc., healthy products with few residual voids can be manufactured without the mechanical grinding process. , improved product yield and lower costs can be achieved. This manufacturing method for titanium alloy powder sintered products can also be applied to titanium powder sintered products. It should be noted that the present invention is also extremely effective for surface shaping of HIP-treated products using alloy powder produced by a rotating electrode method or the like.

[Brief explanation of the drawings] Figure 1 is an optical microscopic photograph of the metal structure of a titanium alloy with a composition consisting of Ti-6A Q-4V after HIP treatment. Figure 2 has the same composition as Figure 1. A titanium alloy made by the method of the present invention was shot peened for 20 minutes. An optical microscope photograph of metal #I texture was taken by projecting a steel ball. Figure 3 shows a titanium alloy having the same composition as Figures 1 and 2. Figure 4 is a photograph of the metal structure of a shot-peened steel ball produced by the method of the present invention shot for 40 minutes using an optical microscope. 2 old 77lI L111j Figure 4

Claims (1)

[Claims] When manufacturing titanium alloy powder sintered products, the sintered titanium alloy manufactured through the processes of mixing constituent metal element powders, compacting, and vacuum sintering is heated to α of 700°C or higher up to the β transformation point temperature.
A method for manufacturing a titanium alloy powder sintered product, which comprises applying pressure in the +β2 phase region, removing voids remaining in the surface layer of the semi-finished product by shot peening, and finishing the surface.