中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 17 No. 1 January 2007 |
（1. School of Material and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China;
2. School of Materials Science and Engineering, Central South University,
Changsha 410083, China）
Abstract: Heavy duty engine valve head was prepared by Ni76Cr19AlTi alloy. It was coated by cobalt-base alloy on the surface to promote its wear-resistance. Hardness tester, metallograph, scanning microscopy, energy spectrum and X-ray diffraction were used to analyze the mechanical properties, the microstructure of the welds and the coated layer of cobalt-base alloy. The results show that the grains are obviously coasened in the side of Ni76Cr19AlTi alloy in the welds and it contains a typical dentritic structure in the side cobalt-base alloy. It is found that micro-strain in weld is stronger than that in heat-effected-zone. Micro-strain in nickel-base alloy is stronger than that cobalt-base alloy. There are not obvious imperfects in the weld. Hardness in cobalt-base alloy is more than 390HV and the major carbides in cobalt-base alloy are Cr7C3 and W2C.
Key words: engine valve; nickel-base alloy; cobalt-base alloy; plasma cladding; microstructure; mechanical property
