Chapter 9 - Alloy Design for Advanced Manufacturing Processes

Abstract

This chapter focuses on alloy design for specific manufacturing processes. The previous chapters were limited to describing and achieving optimum microstructures in alloys for targeted combination of properties in mill products, which are generally not amenable to fabrication of components using promising manufacturing processes. The illustrative example approach in this chapter considers three such distinct manufacturing processes: (1) superplastic forming (SPF), (2) friction stir welding (FSW), and (3) additive manufacturing (AM). The principles of microstructural design for SPF, FSW, and AM are based on the same metallurgy and mechanisms as for alloy design discussed in earlier chapters in detail. SPF is a well-established solid-state manufacturing technology for unitized structures. The forming temperature is kept constant during the operation and gas pressure is adjusted to complete the forming cycle. The alloy design approach for SPF primarily focuses on fine grain size and thermal stability of microstructure. FSW started in 1995 but is still considered a relatively new joining technique because of the long history of other welding techniques. It has developed as a breakthrough joining technique for nonweldable high strength aluminum alloys. Currently, it is applied to existing aluminum alloys for a wide range of applications. The discussion on FSW in this chapter is focused on a few examples of the joint efficiency and its linkage to the physical metallurgy of the alloys. This discussion becomes the basis for suggesting future directions of alloy design to capitalize on the fundamental attributes of this process. The last process considered in this chapter is AM. Although AM of metallic parts is the current rage in manufacturing community for printing components with complex design, the processes themselves have been in existence from 1980s in the name of rapid prototyping. The focus in this chapter is limited to laser-based powder-bed technologies (LBPBT). The context of alloy selection is discussed with the potential pathways for applying design of alloys with hierarchical microstructure for LBPBT. A key message is that the best potential for high-performance engineering application lies in an integrated approach of alloy and process design for each manufacturing process. Of course, the challenges of qualifying a combination of new process and new alloy increase multifold, but this has to be accepted for accelerated progress.