Development of Rolling Technology for an Iron-Based Shape-Memory-Alloy

Abstract

Abstract. Low cost Fe-Mn-Si based shape memory alloys (SMA) have drawn much attention during the last two decades as a cost-effective alternative to the expensive Ni-Ti based SMA. In particular, the alloy Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (mass%), which has been developed at Empa shows very promising properties with regard to potential commercial applications in civil and mechanical engineering. This alloy has a higher reverse transformation temperature and larger thermal hysteresis in comparison to the Ni-Ti based alloys, which is adequate for producing stable recovery stresses at room temperature. Furthermore, recovery stresses of up to 300 MPa after heating to only 160 °C can be achieved without so-called 'training' treatment. Furthermore, the alloy can be easily and cost effectively produced under standard air melting and casting conditions. For availability of these heavily microstructure dependent skills for civil and mechanical engineering, e.g. as prestressing elements in concrete structures or coupling/clamping devices, a process chain for manufacturing is necessary. Therefore, a hot and cold rolling technology for strip production with thermal heat treatment processes was developed at TU Bergakademie on base of experimental simulation results. The last one helps to understand the dependencies of deformation parameters, the deformation behavior and their influence to the microstructure evolution in correlation to the recovery. This paper discusses the basic material properties, recovery stress formation behavior and finally the feasibility of the alloy as reinforcing elements in civil engineering applications by using a rolling technology for flat products. IntroductionShape memory alloy (SMA) steels based on the Fe-Mn-Si alloy system are promising candidates for a variety of advanced civil engineering applications, since they have a wide transformation hysteresis, high elastic stiffness and strength and are relatively inexpensive to produce [1]. These advantages make them promising as a cost-effective alternative to conventional NiTi-based SMAs for applications requiring high shape memory stresses, e.g. constrained recovery applications such as external confinement for reinforced concrete columns [2] or as prestressing reinforcement in prestressed concrete [3;4].The shape memory effect in Fe-Mn-Si alloys is a result of a mechanically induced phase transformation from austenite (face centered cubic phase, γ) to martensite (hexagonal close packed phase, ε) and its reversion upon heating [5]. Under pure mechanical loading, stress induced martensite forms and the resulting strain can exceed the elastic strain limit of the alloy. This strain can be recovered by the reverse transformation due to the same crystallographic path of the two transformations [6].

Key Factors Achieving Large Recovery Strains in Polycrystalline Fe–Mn–Si‐Based Shape Memory Alloys: A Review

“…Furthermore, effects of other alloying elements such as interstitial atoms, rare earth elements, copper, and cobalt on SME were investigated in the Fe – Mn – Si‐based SMAs. In addition to the SME, a lot of researches on factors influencing the recovery stress of Fe – Mn – Si‐based SMAs have also been done . Especially, note that to obtain a good SME Si addition is indispensable in polycrystalline Fe – Mn – Si‐based SMAs, and the content of 5–6 wt% should be guaranteed.…”

Key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys

“…discovered a giant recovery strain of 9% in a monocrystalline Fe-30Mn-1Si alloy [17]. For the purpose of practical applications, polycrystalline Fe-Mn-Si based SMAs have to be manufactured and are generally subjected to processing techniques, such as forging [18], rolling [19][20][21], and drawing [22]. Unfortunately, the processed polycrystalline Fe-Mn-Si based SMAs only achieve a low recovery strain of 2-3% after solution treatments at temperatures from 1273 K to 1473 K [18,[23][24][25].…”

Flexural strengthening of structural concrete with iron‐based shape memory alloy strips

“…Prototype product development resulted in ribbed bars with a circular cross section as well as ribbed strips. The definition of adequate rolling parameters was one important aspect . The mentioned products are either embedded in a shotcrete layer or are applied as a near‐surface‐mounted (NSM) technique .…”