TEM image of Co 46 Ni 27 Ga 27 showing martensite structure and the γ precipitate

1. Computational and Experimental Design of Novel CoNiGa High Temperature Shape Memory Alloys (HTSMAs)Raymundo Arroyave, Texas Engineering Experiment Station, DMR 0805293 Electronic structure and mechanism for martensitic transformation in in Co2NiGa Shape Memory Alloys. • The ultimate goal of the current work is to develop CoNiGa HTSMAs through a combined computational/experimental approach. • The intellectual merits of this transformative research are: • The potential of revolutionizing the field of SMAs, by developing SMAs possessing high TTs, high thermal stability, low susceptibility to creep, aging and cyclic damage as well as good ductility • Transformation of the design process for new HTSMAs through the synergistic experimental-computational approach • The creation of an entirely new family of SMAs, i.e. shape memory superalloys, with very high temperature SM and PE properties. • Research Highlights: • Microstructural degradation mechanisms for the superelastic response of two phase CoNiGa high temperature SMA with the highest reported superelastic temperature were revealed. • A thermally and chemically stable CoNiGa HTSMA composition was discovered with phase transformation temperature of 172 °C and transformation hysteresis of 38 °C. • It was shown for the first time in CoNiGa alloys that Ms temperature linearly depends on the valence electron concentration (e/a) of the matrix, if the Ga content is constant. For a given e/a, the higher the Ga content is, the higher the transformation temperatures become due to the effect of Ga in magnetic properties of the alloys. Electronic structure calculations also corroborate this observation. • Through first-principles calculations, the mechanism for the transformation in CoNiGa SMAs was shown to be fundamentally different from that of other Heusler systems, such as Ni2MnGa. The conventional explanation for the instability of the cubic austenite phase in terms of Fermi surface nesting and formation of pseudo-gaps in the density of states has been put into question. • A full thermodynamic model for the Co-Ni-Ga system over the entire composition and temperature range has been constructed by using experimental as well as ab initio data within the CALPHAD approach. Model predictions have been satisfactorily compared with alloys prepared by the experimental components of this collaboration. Predicted phase diagram in Co-Ni-Ga system at 1000 C and comparison with experiments γ phase TEM image of Co46Ni27Ga27 showing martensite structure and the γ precipitate Martensite Ms temperatures of CoNiGa SMAs with single or multiphase structures as a function of the e/a ratio and Ga content.

2. Computational and Experimental Design of Novel CoNiGa High Temperature Shape Memory Alloys Raymundo Arroyave,Texas Engineering Experiment Station, DMR 0805293 • The broader impacts of the proposed activity are reflected in the following areas: • Maintaining US leading role in active materials research despite the vast amount of recent works at overseas on SMAs • Development of teaching modules for incorporation into undergraduate courses • Helping K-12 students in developing science projects with SMAs • Enriched graduate and undergraduate research experiences in coordination with the new IGERT and Nanomaterials certificate programs • Development of a graduate course in computational materials science • Involvement of underrepresented groups • Disseminating the knowledge generated to both academia and industry through the workshops and symposiums on SMAs, presentations, publications, and a website, and close collaboration with industry. • Broader Impact Highlights: • Five students (including one female and one Hispanic), two M. S., two Ph. D., and one undergraduate are employed in the project. • A course on thermodynamics of materials and applications of computational thermodynamics has been developed and offered during Spring 2008 and 2010. • Ongoing interaction with a local high school for new science projects. Two eighth-grade female students from Harmony Science Academy – a charter school, Shifa Abuzaid and Arsheen Memon received bronze awards in the International Sustainable Energy, Engineering and Environment Project Olympiad (I-SWEEEP) 2010, Senior Engineering Category. I-SWEEEP is a groundbreaking science fair open to middle and high school students. It is the largest science fair event of its kind world-wide. Each year, around 500 projects from 70 different countries competes in I-SWEEP (www.isweeep.org) • The PI and Co-PI have been active in the ISWEEP Olympiad as judge and member of the organizing committee, respectively, for the last two years. Also they have been involved in recruitment activities at Minority Institutions, such as the University of Texas-Pan-American and assisted in the organization of a Materials Camp for Teachers • In the Summer of 2010, the PI hosted two high school teachers as part of the NSF-funded Enrichment Experiences in Engineering (E3) Program at Texas A&M University • The Co-PI has organized four international symposiums and three workshops for oil/gas, aerospace, and automotive industry on SMAs, up to date. • Six research articles have been published, three in press, and one in review (total of 10). Arsheen Memon, when she was taking her award in I-SWEEEP Tameka Whitney – E3 Program Shifa Abuzaid (Left) and Arsheen Memon (Right) with their bronze medals. Dan Barber – E3 Program