Tungsten Copper Contacts Cryogenic Treatment

Cryogenic treatment refers to process the blank at -190℃-230℃, which has a broad application prospect, such as non-ferrous metal, ferrous metal, metal alloy, carbide, plastic, silicate and so on. The basic principle is that in the process of metal hardened to cooling by heat treatment, which produces alloy and carbon dissolved and combined with the formation of austenite(Austenitic is a lamellar microstructure, usually ɣ-Fe solid solution in a small amount of non-magnetic solid solution of carbon) and diffusion; in the cooling process, since the low temperature produce suppress the formation of martensite(The crystal structure of martensite is body-centered tetragonal (BCT). High carbon steel is usually accelerated cooling to obtain such organizations and high strength and hardness of steel is one of the main features of martensite.), the final transition point (Mf) is definitely low.

Austenite is very unstable and easily decomposes at low temperature, so the original defects (pores and internal stress concentration part) and becomes plastic flow structure refinement. Therefore, as long as put the metal at ultra-low temperature, the austenite is converted into martensite, which eliminates the internal stress. In addition, due to the contraction of the tissue volume at ultra-low temperature, Fe lattice constant decreases and the driving force to strengthen the precipitation of carbon atoms, so a lot of martensitic matrix deposited ultrafine carbides. The strength of these ultra-fine crystalline materials will improve and increase the wear resistance and rigidity. And Ultra-low temperature can also be transferred metal atom transport capacity, which makes the atoms can not be separated and become closer.

There are some experiments shows that high-pressure vessel after cryogenic treatment can meet the requirements of the strength of solid propellant rocket; some down-hole equipment for sour oil field after cryogenic treatment can improve the corrosion resistance and the welding cracks; some parts of the alloy cryogenic treatment, volume stability, dimensional stability and strength has been greatly improved.

At present, cryogenic treatment mainly applied in tool steel, non-ferrous metal applications under development step, here we discuss that the tungsten copper contacts cryogenic treatment process conditions affect its properties. Tungsten copper contact is a psudoalloy, which is composed of two kinds of immiscible and has a great difference in physical and chemical properties metals. There is no phase change in the reaction and it is brittle so that it is difficult to adapt conventional heat treatment hardening process to improve its relative performance. Cryogenic treatment is undoubtedly an ideal choice.

Viewed from the micro-structure, after cryogenic treatment, W matrix disperse a large number of Cu phase and the organization has significantly refined, which is due to precipitation of Cu solute in W after cryogenic treatment. In addition, it also can be found that with the increase in the copper content, the segregation phenomenon is also becoming increasing apparently. Copper particles dispersed precipitated tissue thinning, and atomic displacement volume shrinkage, tungsten copper contact density and overall strength has also improved.

While its hardness and strength has greatly improved after cryogenic treatment, and electrical conductivity with increasing tungsten content decreases. This is due to cryogenic treatment makes a lot of precipitated Cu and W form a solid solution, and is proportional to the electrical conductivity of tungsten copper contacts with the copper content. Overall, tungsten copper contacts after cryogenic treatment, may be little alternative to tungsten copper copper-tungsten less, not only improves performance, but also reduce costs.

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