Shape memory alloys (SMAs) with high transformation temperatures can enable simplifications and improvements in operating efficiency of many mechanical components designed to operate at temperatures above 100uC, potentially impacting the automotive, aerospace, manufacturing and energy exploration industries. A wide range of these SMAs exists and can be categorised in three groups based on their martensitic transformation temperatures: group I, transformation temperatures in the range of 100-400uC; group II, in the range of 400-700uC; and group III, above 700uC. In addition to the high transformation temperatures, potential high temperature shape memory alloys (HTSMAs) must also exhibit acceptable recoverable transformation strain levels, long term stability, resistance to plastic deformation and creep, and adequate environmental resistance. These criteria become increasingly more difficult to satisfy as their operating temperatures increase, due to greater involvement of thermally activated mechanisms in their thermomechanical responses. Moreover, poor workability, due to the ordered intermetallic structure of many HTSMA systems, and high material costs pose additional problems for the commercialisation of HTSMAs. In spite of these challenges, progress has been made through compositional control, alloying, and the application of various thermomechanical processing techniques to the point that several likely applications have been demonstrated in alloys such as Ti-Ni-Pd and Ti-Ni-Pt. In the present work, a comprehensive review of potential HTSMA systems are presented in terms of physical and thermomechanical properties, processing techniques, challenges and applications.

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a b s t r a c tFeMnAlNi shape memory alloys were recently discovered to have a small temperature dependence of the superelastic critical stress in a large superelastic temperature window from À196°C to 240°C. In this work, we investigated the effect of B2 nanoprecipitates on the superelastic characteristics of [1 0 0] oriented Fe 43.5 Mn 34 Al 15 Ni 7.5 single crystals under compression, and found that the size, volume fraction and composition of precipitates strongly influence the transformation temperature, superelastic strain, critical stress for stress-induced martensitic transformation and stress hysteresis of the single crystals. The single crystals aged at 200°C for 3 h show 7.2% superelastic strain with the precipitate size of about 6-10 nm. Longer aging times or higher aging temperature reduces superelastic recovery due to the coarsening of the precipitates.

The objective was to compare the efficacy of two experimental Staphylococcus aureus mastitis bacterins and a currently marketed five-isolate-based Staph. aureus bacterin (Lysigin, Boehringer Ingelheim Vetmedica, Inc.) with unvaccinated controls. Forty-seven Holstein-Friesian heifers were randomly assigned to one of four groups such that Group 1 (n=11) received a three-isolate experimental bacterin, Group 2 (n=11) received a five-isolate experimental bacterin, Group 3 (n=14) received Lysigin, and Group 4 (n=11) served as unvaccinated controls. Vaccinations were administered twice 28 d apart in late gestation. All groups were challenged with a heterologous strain of Staph. aureus (ATCC 29740) on days 6, 7, and 8 of lactation. Mastitis score, somatic cell count (SCC), milk culture yield, and total daily milk yield data were collected before and after challenge. All 47 cattle developed a Staph. aureus IMI post-challenge with three animals in Group 1 and one animal in Group 3 clearing their Staph. aureus IMI by the end of the study. However, there was no evidence of a difference between vaccinates and control with regard to Staph. aureus clearance rates post-challenge (P> or =0.214). Cattle vaccinated with Lysigin had a lower mean duration of clinical mastitis and lower total mastitis score post-challenge than controls (P=0.045 and P=0.046, respectively). Overall, there was no evidence that any of the vaccinated groups had a lower mean SCC than control (P> or =0.148) for the tested study days. Likewise there was no evidence that vaccinates had greater milk yield than controls post-challenge (P=0.617). Hence, there was no evidence that the vaccines reliably prevented Staph. aureus IMI, but Lysigin showed benefit in reducing the clinical severity and duration of clinical disease post-challenge. Neither of the experimental bacterins appeared to perform better than Lysigin.