Investigation of Interfaces Between Steel and Vapor Phase Deposited Tungsten by Optical and Electron Microscopy and by Electron Probe Microanalysis
Specific materials requirements such as high temperature strength in combination with corrosion and erosion resistance and limitations in cost and weight often can only be satisfied when a composite material is utilized. A typical example is shown in the form of a thin tungsten layer deposited by the vapor phase process onto the bore of gun barrels to increase their operational life. Initial attempts to plate 4140 steel resulted in flaking-off of the tungsten coating from the substrate but after development of proper pre-treatment procedures of the substrate and of specified deposition temperature, flow ratios and flow rates, firm mechanical bonds between tungsten and substrate were obtained. Requirements for firm bonds are the absence of surface oxide films, small differences in thermal expansion coefficients, interdiffusion of the two metals into each other and other factors.