Development of Fe-based shape memory alloys associated with face-centered cubic-hexagonal close-packed martensitic trans
- PDF / 4,853,994 Bytes
- 10 Pages / 613 x 788.28 pts Page_size
- 55 Downloads / 134 Views
I.
INTRODUCTION
IN Parts I and II, tL2] the shape memory behavior and the related transformation characteristics were addressed for newly developed Fe-based shape memory alloys associated with face-centered cubic-hexagonal close-packed (fcc-hcp) martensitic transformations. The purpose of this article is to correlate the macroscopic properties with microstructures involved in the martensitic transformations and deformation modes in these alloys. As might be expected, the microstructural characteristics of e martensite and their correlation with the shape memory effect (SME) should be quite evident and straightforward since the crystallography of fcc-hcp martensitic transformation is particularly simple and has been well established since the early 1950s. ]3,4,51 Indeed, the origin of the shape memory of e martensite can be simply attributed to the preferential multiplication of a single type of Shockley partial dislocation upon transformation; these accumulate a stress field which assists the partial dislocations when moving backward to restore the original orientation of the parent phase upon reverse transformation. In other words, the complete SME is believed to be associated with a stress-induced fcc-to-hcp transformation. This topic has been studied in detail by Sato et a1.[6'7"9]and Enami et al.[8] in single crystals of Fe-Mn and Fe-Cr-Ni stainless steels. In practical situations, however, the microstructural characteristics of the transformation, either thermally induced or strain-induced, are much more complicated due to the influence of various physical factors, especially in polyci'ystalline alloys, where the local stress state may be complex. For these conditions, various deformation modes (e martensitic transformation, a ' martensitic transformation, and plastic slip, basically) may be expected to occur concurrently. Therefore, it is of fundamental interest to characterize the microstructures of these various physical processes and their contributions to the SME in the J.H. YANG, Research Associate, and C.M. W A Y M A N , Professor, are with the Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801. Manuscript submitted March 18, 1991. METALLURGICAL TRANSACTIONS A
polycrystalline alloys conditions. II.
under
different experimental
EXPERIMENTAL
Three groups of experimental alloys were studied. See Parts I and II tL2] for the details about chemical compositions and various transformation temperatures. In this article, these three groups of alloys are cited as alloys A (alloys 1, 2, and 3 in Part II1]), B (alloys 4 through 7 in Part I[1]), and C (alloy 8 in Part It1]), respectively. The Ms temperatures are - 3 0 0 ,
Data Loading...
