Evaluation of the pumping performance of combinations of Ti–Zr–V–Hf alloy nonevaporable getter coatings with different morphologies, activation protocols controlled at cryogenic temperatures

Abstract

The pumping performance of a range of Ti, V, Zr, and Hf alloy nonevaporable getter (NEG) coatings of order 5 μm thickness and with different modular structures has been investigated. For equal atomic percent Ti–Zr–V–Hf quaternary alloys, dual (columnar layer on the dense layer) coatings gave higher sticking probabilities than columnar and dense morphologies. The same alloy provided the highest sticking probability, followed by the Ti–Zr–V tertiary alloy, and then singular Zr. For a 24 h activation time, single element Zr coatings were shown to require an activation temperature of 300 vs 250 °C for the other alloys. H2 and N2 sticking probabilities increased by a factor of 100 and N2 terminal capacities by a factor of 1000, in the range 150–300 °C. For the dual coated Ti–Zr–V–Hf quaternary alloy at an activation temperature of 140 °C, H2 sticking probabilities increased by a factor of 2 when the activation time increased from 1 to 7 days and that of N2 increased by a factor of 6. The factor of 100 increase in measured sticking probability at LN2 temperature, compared to room temperature, to a value of 0.5 for H2, is transient in nature. Further investigations into this behavior are planned.