PREPARATION OF CrN-Ni COMPOSITES BY HOT PRESS SINTERING

摘要

Cemented carbide (WC-Co) is used in cutting tools such as drills and end mills. However, since relatively scarce metals such as W and Co are expensive, development of alternative materials with comparable mechanical properties and chemical stability is required. For this purpose, CrN-Ni, consisting of a CrN ceramic and a Ni binder, is considered to be a promising material because thin films of CrN exhibit high hardness, oxidation resistance and corrosion resistance. In this study, sintered CrN-Ni composites were prepared from a mixed powder of Cr_2N and Ni. The Cr:Ni molar ratio was varied from 10:0 to 8:2. In order to obtain the CrN phase from Cr_2N, the mixed powder was sandwiched between layers of Mg_3N_2 powder, which decomposes at elevated temperatures to produce nitrogen. The green compacts were subjected to hot-press sintering under a pressure of 70 MPa between upper and lower graphite punches. After evacuation of the hot press down to 3.6 Pa, nitrogen gas was introduced at a pressure of 3.3×10~3 Pa. The sintered bulks were characterized by X-ray diffraction. The CrN bulk sintered at 1000 ℃ was of a single phase with a high density (6.11 g cm~(-3)), and the Vickers hardness was 1000 kgf mm~(-2). Moreover, the CrN-Ni composite sintered at 1200 ℃ obtained core-rim structure with CrN grains surrounded by nickel.