Ta10W alloy reflux coil will be seriously eroded by potassium at 980 ° C, but Ta8W2Hf alloy will not suffer any erosion at 1315 ° C exposure for 2000h. The reason is that the O element in Ta10W is dissolved in the tantalum matrix during the processing test, and the high oxygen content in the grain boundary region leads to the preferential corrosion of alkaline metal on the intergranular region and the formation of cavitation. After the addition of Hf element, a stable oxide is formed, and the oxide is almost not corroded by alkaline metals, thus significantly improving the corrosion resistance of the alloy.
As refractory metal alloys, TaW series alloys have a high melting point and are easy to oxidize, which are generally prepared by vacuum electron beam melting, and a small amount by powder metallurgy. The melting point of Hf is 2222℃, which is nearly 800℃ lower than the melting point of Ta, near the melting point of Hf, the vapor pressure of Hf is 3 orders of magnitude higher than that of tantalum, so Hf melts before Ta in vacuum melting, and is extremely volatile, so for TaWHf series alloys, the addition method of hafnium and the preparation method of the alloy will affect the final composition of the alloy. The United States uses the method of electron beam melting and electric arc furnace melting, the high melting point, difficult to volatilize Ta, W is alloyed with electron beam melting, and then Hf is added in electric arc furnace melting, combining the two melting methods, not only to achieve the purification effect of electron beam melting, but also to take advantage of the advantages of electric arc furnace rapid melting, to avoid the problem of uncontrollable volatilization of Hf elements.
A method for increasing hafnium content in tantalum-tungsten alloy is provided. The method is timely filled with argon protection during the cooling process of high temperature vacuum sintering, effectively reducing the volatilization of hafnium, and different melting speeds are adopted in the two rapid vacuum electron beam melting processes to avoid a large number of hafnium elements being extracted and volatilized, and the final mass content of hafnium in tantalum tungsten alloy is more than 80% of the design content, greatly improving the hafnium content in tantalum tungsten alloy. The method of increasing the hafnium content in tantalum tungsten alloy is characterized in that the mixing equipment used in step 1 is a mixing machine, and the mixing time is 24h. The mixer is used for full mixing to promote the full mixing of tantalum powder, tungsten powder and hafnium powder.
