Due to its high density, high melting point, good plasticity, especially excellent corrosion resistance and high temperature mechanical properties, tantalum-tungsten alloy is widely used in the fields of high temperature, chemical industry, aerospace and electronics. However, its poor oxidation resistance greatly limited its application.
It is an important way to improve the oxidation resistance of tantalum-tungsten alloy by matrix alloying and surface engineering. Matrix alloying technology is mainly limited by the amount of alloying elements, especially some precious metals are expensive to use, the cost is too high, and has a great impact on the overall performance of the matrix materials. At present, the latter mainly improves the oxidation resistance of the material surface through coating protection technology, but this technology is easy to be restricted by the binding strength of the coating and the substrate, especially the coating is easy to flake when subjected to fatigue load, which has a destructive effect on the substrate material.
The double glow plasma surface metallurgy technology can prepare the diffusing layer with gradient distribution of elements, and realize the firm metallurgical combination with the substrate. In this paper, the surface of tantalum-tungsten alloy was carburized and impregnated with hafnium by this technology, and the technological parameters, morphology, phase, hardness and oxidation resistance of the alloy layer were studied.
1. The graphite insulation cover is used as the tubular electrode producing hollow cathode effect to realize the infiltration of C and Hf on the surface of ta-w alloy at the same time; After different process exploration, TaC and Ta2C coating with a small amount of HfC was prepared on the surface of ta-w alloy. The hardness value of the coating was up to about 1700HV. The C content in the alloy layer shows a gradient decrease trend, which is consistent with the hardness value.
2. Hf alloy layer was firstly prepared by glow plasma infiltration Hf on the surface of ta-w alloy with deep well electrode structure, and Hf was distributed in a gradient in the alloy layer. The thickness of alloy layer increases with the increase of Hf infiltration temperature. The thickness of alloy layer is 5 muon for 5h at 1400℃, 45 muon for 6h at 1600℃ and 140 muon for 12h at 1700℃.
3. After Hf alloy layer was prepared on ta-w alloy surface, the oxidation resistance was greatly improved, and the higher the metal infiltration temperature was, the thicker the layer was, and the more obvious the effect was. The anti-oxidation mechanism of Hf alloy layer was preliminarily analyzed because the generated HfO2 film was quite dense and prevented oxygen ions from diffusing into the matrix. On the other hand, HfO2 alleviates the stress generated during the formation of oxide film and delays the cracking and peeling time of oxide film.
