Microstructure and mechanical properties of the PM precipitation-hardening alloy N07626: effect of HIP temperature and solution annealing

Abstract

The microstructure and mechanical properties of the precipitation-hardening powder metallurgy Ni-base alloys UNS N07626 are investigated. The material was compacted by hot isostatic pressing and solution treated adopting distinct conditions to reveal the effect of processing temperature on material properties. The microstructure is analysed by scanning electron microscopy, optical microscopy and electron backscatter diffraction and energy-dispersive X-ray spectroscopy. The prior particle boundaries (PPBs) are related to the presence of thermally stable nanometric Nb-carbides and aluminium oxides. An increase of processing temperature conditions is associated to a slight decrease of mechanical strength and to an appreciable improvement of toughness, as suggested by Instrumented V-Notch Charpy experiments. This behaviour is attributed to the reduction of the density of PPBs precipitates acting as void-nucleating sites in a micro-ductility mechanism. The precipitates’ density is related to a limited grain growth and the resulting separation of PPBs from grain boundaries.

Keywords:

• Nickel alloys
• Hot isostatic pressing
• Microstructure
• Prior particle boundaries
• Microductility