Titanium alloys respond well to heat treatment be it to increase strength (age hardening), reduce residual stresses, or minimize tradeoffs in ductility, machinability, and dimensional and structural stability (annealing). This chapter describes the phase transformations associated with these processes, explaining how and why they occur and how they are typically controlled. It makes extensive use of phase diagrams and cooling curves to illustrate the effects of alloying and quenching on beta-to-alpha transformations and the conditions that produce metastable phases. It also examines several time-temperature-transformation diagrams, which account for the effect of cooling rate.

Nickel-base alloys are generally used in harsh environments that demand either corrosion resistance or high-temperature strength. This article first describes the general welding characteristics of nickel-base alloys. It then describes the weldability of solid-solution nickel-base alloys in terms of grain boundary precipitation, grain growth, and hot cracking in the heat-affected zone; fusion zone segregation and porosity; and postweld heat treatments. Next, the article analyzes the welding characteristics of dissimilar and clad materials. This is followed by sections summarizing the various types and general weldability of age-hardened nickel-base alloys. The article then discusses the composition, welding metallurgy, and properties of cast nickel-base superalloys. Finally, it provides information on the welding of dissimilar metals, filler metal selection for welding clad materials and for overlay cladding, service conditions during repair, and welding procedural idiosyncrasies of cobalt-base alloys.