The bottleneck of expanding the titanium alloy market is that it is difficult to extract, melt, and machine titanium, resulting in high production costs. The production cost of titanium ingots is about 30 times that of steel ingots of the same weight and 6 times that of aluminum ingots. Among them, the cost of producing titanium sponge from ore to magnesium reduction is about 20 times that of iron. At present, the cost of industrial pure titanium per ton is about 7.5 to 10 $ / kg, and the production cost of aerospace titanium alloy is as high as 40 $ / kg_.
Therefore, the cost reduction is mainly to reduce the production cost of industrial pure titanium and the manufacturing and processing cost of titanium and titanium alloys. In order to reduce the cost of titanium alloys, foreign countries have vigorously developed the near-net shape process of titanium alloy without cutting and less cutting. Powder metallurgy technology is one of such near-net shape processes.
There are currently three main methods for manufacturing titanium alloy parts:
- Traditional forging materials processing;
- Powder metallurgy.
Forging for material processing, the material performance is excellent, but the waste is large, the processing volume is high, the cost is high, and it is difficult to obtain products with complex shapes; casting can obtain net shapes with complex shapes or near net shapes, and the cost is lower, but casting Defects such as segregation, loosening, and shrinkage of the composition of the material in the process are difficult to avoid, and the material performance is low. The powder metallurgy technology of titanium alloy overcomes the shortcomings of these two methods, and at the same time has their advantages. Therefore, domestic and foreign researchers have carried out a lot of work on the preparation of titanium alloys by powder metallurgy technology. This article gives a brief introduction to several powder metallurgy technologies for the preparation of high-performance titanium alloys and their applications in foreign research and development in recent years.
- 1 New powder metallurgy preparation technology
- 1.1 Metal Injection Molding (MlM)
Metal powder injection molding (MIM) technology, as a near-net forming technology, can produce high-quality, high-precision complex parts, and is considered to be one of the most advantageous forming technologies. The use of MIM to manufacture titanium and titanium alloy near-net shape parts can greatly reduce processing costs. It is estimated that the current production of titanium MIM parts worldwide is 3 to 5 tons per month. With the improvement of the process of preparing titanium powder and the reduction of powder cost, the production volume of titanium alloy injection molded parts is increasing. Japan first used MIM technology to produce Ti-4wt% Fe alloy sports splint. At present, the largest titanium powder injection molding production plant is Injex in Japan, which produces about 2 to 3 tons per month. Titanium MIM products have been used in golf heads, automatic automobiles, medical equipment, dental implants and watch straps.
The titanium alloy case made by Hitachi Metal Precision and Casio Computer in Japan won the MIM Award at the International Powder Metallurgy Conference in 1999. The watch can still operate normally at a water depth of 200m. Some universities in Japan used Sumitomo Sitix gas atomized spherical titanium powder to prepare Ti-6Al-4V, Ti-12Mo, Ti-5Co alloys by MIM method.
The material properties are better than those made by conventional powder metallurgy technology under the same conditions, and fully reach the level of smelting and forging materials with the same composition. In addition, a Japanese company uses injection molding to manufacture complex titanium-iron alloy parts, such as sole nails for track and field running shoes. In this method, powder of titanium-iron alloy (Ti-5wt% Fe) and organic binder are mixed and injection molded at a pressure of 196MPa. After degreasing at 550 degrees, vacuum sintering is performed at 1000-1400 degrees and 1.33 × 10 Pa. Compared with the molybdenum alloy shoe spikes, the titanium iron alloy spikes made in this way have improved abrasion resistance and impact resistance. And the weight is reduced by 45%.