The effect of stress-induced martensite aging in tension and compression on B2–B19′ martensitic transformation in Ni_50.3Ti_32.2Hf_17.5 high-temperature shape memory alloy

Abstract

The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni50.3Ti32.2Hf17.5 polycrystals with nanosized H-phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth.

The Effect of Subsequent Stress-Induced Martensite Aging on the Viscoelastic Properties of Aged NiTiHf Polycrystals

“…SIM-aging results in a decrease in M f and A s TTs by 15-20 K. Thus, an increase in MT temperature interval ∆ 1 (MT diffusion) is observed (Figure 3). The same MT diffusion upon stress-assisted cooling/heating cycles was observed in type (II SIM ) samples, which were preliminarily aged at 773 K for 3 h [6]. This increase in MT temperature interval is the result of an increase in stored elastic energy during direct MT due to a high density of compound twins and detwinning processes.…”

“…The analyses of the obtained results and their comparison to the experimental data obtained for polycrystals with the same chemical composition-Ni 50.3 Ti 32.2 Hf 17.5 (at.%)aged at 773 K for 3 h [6] demonstrate that the effect of SIM-aging on viscoelastic and functional properties depends on the initial microstructure of heterophase alloys (Table 1). The DMA properties of both polycrystal types (type (I) and type (I SIM ) samples) are presented as average values for both cooling and heating and are compared to the polycrystals aged at 773 K for 3 h with (type (II SIM ) samples) and without (type (II) samples) subsequent SIM-aging (Table 1).…”

“…To perform the full analyses of obtained results, we must compare them with the data from our previous work [6], where polycrystals with the same chemical composition-Ni 50.3 Ti 32.2 Hf 17.5 (at.%)-underwent SIM-aging following the same regime. However, these polycrystals were preliminarily aged in austenite at 773 K for 3 h, so they possessed a different microstructure compared to the polycrystals in the present work.…”

“…The increase of aging temperature from 773 K to 873 K for 3 h results in an increase in H-phase particle size from 10-15 nm [6] to 70 nm. In addition, the particle shape changes from spherical to spindle with the increase in aging temperature.…”

“…These particles do not undergo martensitic transformations but deform elastically, strengthen the materials, and increase transformation temperatures. The following SIM-aging was carried out using a dilatometer (IMRS-1, Microsplav, Tomsk, Russia), after which DMA (dynamical mechanical analysis) was carried out, with the same regime as in previous work [6]. First, the sample was heated to a temperature of T = 533 K > A f (austenite finish temperature).…”