a cold - worked titanium material subjected to isostatic material and a backing plate are brought into contact with each other and subsequently hot - pressing . by such working the titanium material and the backing plate are bonded with each other by mutual diffusion and simultaneously the titanium material is recrystallized . the isostatic pressing is performed under a pressure of 50 to 200 mpa at a temperature of 300 ° to 450 ° c . the surface of the titanium material is preferably subjected to a surface roughening treatment to provide with a roughness level of 6s to 12s prior to the isostatic pressing .