炭素鋼とチタン箔の拡散接合と表面窒化同時処理の検討

摘要

The purpose of this study is the development of simultaneous processing of diffusion bonding and surface nitriding. Carbon steel was used as the base material. The surface was nitrided to a 20-μm-thick titanium foil. The sample was arranged in the order of carbon steel, titanium foil, and Al_2O_3 powder (diameter = 1 μm) and placed in N_2 gas in a furnace to undergo simultaneous diffusion bonding and surface nitriding. These processes were carried out at a processing temperature T of 1100~1250 K and processing pressure P of 0.5 Mpa (processing time = 4.8 ks). Because no defect was observed in the bonded interface, it was confirmed that a sufficiently suitable joint can be obtained under these processing conditions. The surface hardness was observed to increase with the increase in processing temperature; it reached approximately HV1600 at 1250 K. The surface of the titanium foil, which had been simultaneously processed at 1250 K, consisted of a single phase of TiN. The results of the ball-on-disc-type wear test revealed that the surface, which had been processed at 1250 K, was hardly worn by the TiN layer.%チタンの窒化物である窒化チタン（TiN）は，熱膨張係数が鉄鋼材料に近く，高硬度で耐食性，耐摩耗性に優れているセラミックスであり，これを金属の表面にコーティングすることで，金属の表面硬度および耐摩耗性を向上させる窒化チタン薄膜付与材が研究・実用化されている~(1-3)）．しかし，このような薄膜付与材は，薄膜形成過程から不可避的に存在するピンホール欠陥~(4-6)），マイクロクラックなどに起因する薄膜自身の割れや，はく離，下地金属の孔食などにより，形成した膜とのすき間腐食へと進展することが原田と考えられている局部腐食が発生し，下地金属が腐食されることにより薄膜の保持が困難となることが報告されている~(7,8)）．