The effect of thermal cycling on the thermoelastic martensitic transformation in a Cu-Zn-Al alloy
- PDF / 2,271,538 Bytes
- 5 Pages / 603.28 x 788 pts Page_size
- 58 Downloads / 268 Views
I.
INTRODUCTION
THEeffects of transformation cycling on the nature of the thermoelastic martensitic transformation in ferrous alloys has been extensively studied. 1'2 Changes in the M, temperature and the extent of thermal hysteresis are attributed to the order-disorder reaction in ferrous alloys. 2 This is in contrast to the case of the thermoelastic martensitic transformation in the beta brass system where the alloy is initially completely ordered after quenching, and remains ordered through the transformation. While there have been several studies which bear on the effects of thermal cycling on the subsequent martensitic transformation in beta brass systems, the data are. sparse and the results contradictory. Earlier work 3 reported that in a Cu-40.6 wt pct Zn alloy the M~ temperature increased about 5 ~ after 50 thermal cycles. However, later work4 on a Cu-39.63 wt pct Zn alloy reported that the M, temperature decreased about 3 ~ after 20 thermal cycles. Moreover, it is clear that no detailed and systematic studies on the effect of thermal cycling on the martensitic transformation in beta brass systems have yet been reported. The purpose of this study is to examine in detail the effect of thermal cycling between the MI and AI temperatures on the thermoelastic martensitic transformation in a Cu-Zn-AI alloy. The transformation was described by its characteristic temperatures, Ms, MI, As, AI, and thermal hysteresis behavior as determined by electrical resistance vs temperature measurements and the morphology of the transformation by examining optically the surface relief during thermal cycling. II.
EXPERIMENTAL METHOD
Specimen preparation. The alloy studied had a nominal composition of 29 wt pct Zn, 3 wt pct AI, and the balance JIAN-CHUN LI, formerly Visiting Scholar, Department of Materials Engineering, Rensselaer Polytechnic Institute, Troy, NY, is now at the Central-South Institute of Mining and Metallurgy, Changsha, People's Republic of China. G.S. ANSELL is Dean of Engineering, Rensselaer Polytechnic Institute, Troy, NY 12181. Manuscript submitted March 12, 1982.
METALLURGICALTRANSACTIONSA
Cu. The alloy composition was defined on the one hand to maintain an electron concentration of 1.4 to stabilize the beta phase and on the other hand to obtain transformation near room temperature for experimental convenience. The alloy was prepared by melting Cu (99.99 pct) powder, Zn (99.9 wt pct) ingot, and A1 (99.999 pct) wire in a sealed quartz tube under an argon atmosphere. After melting and solidification, the ingot was annealed in the quartz tube at 850 ~ for one week. After annealing the ingot was cold rolled into a l-mm thick strip. To form the beta phase these strips were heated in air at 850 ~ for five seconds (to limit Zn loss during heating) and then quenched into an iced 10 pct NaOH solution. The strips were then electropolished in orthophosphoric acid at room temperature to remove approximately 0.1 mm from each surface, removing oxides and possible surface dezincafication. After electropolishing, some
Data Loading...
