Martensitic Transformation and Shape Memory Effect in Ausaged Fe-Ni-Si Alloys.

Abstract

Martensitic transformations in the Fe-(24-30)Ni-(5-8)Si (mass%) alloys have been investigated by means of optical and transmission electron microscopy, differential scanning calorimetry and hardness-testing. The Ms temperature is decreased by Si addition and the morphology of martensite is mainly lenticular in the unaged specimens. However, a pronounced decrease in the Ms temperature and a change in the martensite morphology from the lenticular to the thin plate type are observed on ausaging at 400°C. The increase in austenite hardness, the decrease in the Ms temperature and the increase in the tetragonality of martensite after ausaging at 400°C are clarified as due to the formation of nanoscale particles of gЈ-(Ni,Fe) 3 Si with the L1 2 structure during ausaging at 400°C. The Fe-Ni-Si alloys that form thin plate martensite show the shape memory effect, which arises from the reverse transformation of stress-induced martensite to austenite. Precipitation hardening of the austenite phase by fine gЈ particles during ausaging improves the degree of shape recovery.

Effect of Si on austenite stabilization, martensite morphology, and magnetic properties in Fe-26%Ni-x%Si alloys

“…They also found that the γ-parent phase, which transformed to the thin plate martensite, showed short-range ordering in the L1 2 structure. In addition, Himuro et al [13] found that the martensite morphology changes from lenticular to thin plate martensite with increasing ausaging time in Fe-25%Ni-7.5%Si alloy. According to their conclusion, the formation of coherent γ-(Ni,Fe) 3 Si precipitates causes the formation of thin plate martensites.…”

“…Nishiyama describes stabilization of austenite as such a transformation that occurs difficult from austenite to martensite and also classified the stabilization of austenite in three subclasses as chemical, thermal, and mechanical stabilization [4]. As well, there are considerable studies on austenite stabilization and martensite morphologies of Fe-based alloys [6][7][8][9][10][11][12][13]. Gungunes et al [6] examined the influence of thermal stabilization in an Fe-24.5%Ni-4.5%Si alloy.…”

Microstructure, hyperfine interaction and magnetic transition of Fe-25%Ni-5%Si-x%Co alloys

“…From this result, we can say that addition of Co to Fe-%25Ni-%5Si alloy causes the formation of lenticular martensite. It is well accepted that the martensite morphology is dependent on many factors, such as alloy composition [4,5,7], austenite grain size [19], ausaging [2,20], and martensite formation temperature [7,16], however no one has shed light on the reason why morphology exists in ferrous α martensite so far.…”

“…It is also well known that the plastic deformation of austenite can induce martensitic transformation in Fe based alloys and martensitic transformation can be also induced under different external forces such as hydrostatic pressure and magnetic field [1][2][3]. The elements constituting the alloy is one of the important factors affecting the characteristics of martensitic transformation such as hardness of austenite, morphology of martensite, effect of shape memory and magnetic properties of alloys Hyperfine Interact (2016) 237:11 [4][5][6][7]. For instance, even a small amount of Si, Mo or Co addition changes the martensite morphology, magnetic properties and hardness of the alloy [4,6,8,9].…”

Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel

“…It is known that microstructural factors like distribution of carbides, as well as characteristics of the martensitic matrix, play important roles in optimizing the properties of high-speed steel such as hardness, wear resistance, fracture toughness, and thermal-fatigue behavior. It is also well known that the martensite morphology of HSS depends on austenitizing temperature and its holding time, prior deformation of the austenite matrix, chemical composition of alloys, and the cooling rate [7,8]. A lot of studies have been performed on the effects of austenitizing conditions on the microstructure of high-speed steel.…”