Interstitial-Free Bake Hardening Realized by Epsilon Martensite Reverse Transformation
- PDF / 2,405,643 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 74 Downloads / 186 Views
High-entropy alloys (HEAs) with multi-principal elements have brought about a large degree of freedom in alloy design that can be utilized in the everlasting pursuit for optimal strength-ductility combinations.[1,2] The drastically enlarged compositional space has enabled the accumulation of multiple strengthening mechanisms.[3–7] Amongst them, strain-induced martensitic transformation is especially effective, promoting strength while simultaneously preserving decent ductility.[8] Thus, both face-centered cubic (FCC) and refractory body-centered cubic (BCC)-based metastable HEAs have been designed where significant improvement in mechanical performances were consequently achieved.[9,10] In terms of the FCC-structured metastable HEAs, more recent literature also focuses on providing quantitative design principles, characterizing defect substructure evolution features, and exploring more enhanced properties.[11–14] Although these systematic investigations have advanced the physical insights into the forward FCC
SHAOLOU WEI, MENGLEI JIANG, and CEMAL CEM TASAN are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Contact e-mail: [email protected]. Manuscript submitted April 26, 2019. Article published online July 2, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
austenite-to-hexagonal closed packed (HCP) martensite transformation, the reverse transformation, on the other hand, remains comparatively less explored and unutilized. To this end, we investigate the mechanical property benefits of thermally-induced HCP-martensite-to-austenite reverse transformation in metastable HEAs. The underlying motivations for this study are two-fold: (1) HCP-martensite has been recognized to possess relatively low thermal stability. Lee et al.[15] for example, reviewed that the austenite start temperature (As point) decreased monotonically from ~ 200 C to ~ 150 C as a function of increasing Mn content from 15 to 30 wt pct. Such a low transformation temperature range raises the possibility of feasible thermal processing opportunities similar to bake hardening (BH) treatment, which has not yet been explored; and (2) classical BH treatment in interstitial strengthened Fe- or Al-based alloys involves thermally-assisted segregation of interstitials to dislocation sites, creating a strengthening effect due to the enhanced solute pinning.[16,17] However, it often inevitably results in cumulative ductility compensation because of the deficiency in dislocation multiplication, leading to the deterioration in strain-hardening capability. A bake-reversion treatment that aims at strain-induced martensite reversion, instead of interstitial segregation, should in principle resolve this negative effect. To explore this processing space, we have exploited an interstitial-free Fe45Mn35Co10Cr10 (nominal composition in at. pct) HEA as a model system and examined the proposed concept. Master HEA was fabricated from pure elements through vacuum induction melting followed by hot-rolled to 50 pct thi
Data Loading...
