Nonbasal plane defects in 18r martensite and the effect of abnormal defects on thermoelastic martensitic transformation

Abstract

This investigation, using a Cu-26.4 pct Zn-4.8 pct Al (wt pct) alloy, was carried out to provide more detailed and accurate information on the crystal defects in martensite. By comparing direct-quenched and step-quenched specimens, it has been found that some abnormal defects of martensite, such as nonbasal plane (NBP) planar defects and dislocations, often exist in the martensite obtained by direct quenching. Trace analysis showed that the NBP planar de-fects are often located in the -125 plane of the martensite lattice. High-resolution electron microscopy (HREM) has revealed that the NBP planar defects resulted from basal plane stack-ing faults which break off inside the plate of martensite.In situ observations during heating in the transmission electron microscope (TEM) have proved that martensites which have a great amount of abnormal crystal defects are stable even when heated to high temperature, and the existence of abnormal defects may be one of the reasons for the stabilization of martensite.