TAMU-UIB collaboration: characterization of Ni-Ti-Zr and Ni-Ti-Hf high temperature shape memory alloys A.Evirgen 1, I. Karaman 1, R. Santamarta 2, J. Pons 2 1. Dept. of Mechanical Eng., Texas A&M University, TX, USA 2. Dept. of Physics, Univ. Balearic Islands, Palma de Mallorca, Spain

Activity in the framework of IIMEC in 2011 PhD Student Exchange Activity: TAMU – UIB Summer research stay of ALPER EVIRGEN (I. Karaman’s PhD student) in UIB. July 2011 Financed by IIMEC Research topic: Study of (Ni-rich) Ni-Ti-Zr and Ni-Ti-Hf HTSMAs

Activity in the framework of IIMEC in 2011 PhD Student Exchange Activity: TAMU – UIB Summer research stay of ALPER EVIRGEN (I. Karaman’s PhD student) in UIB. July 2011 Financed by IIMEC Research topic: Study of (Ni-rich) Ni-Ti-Zr and Ni-Ti-Hf HTSMAs NiTi: T M ~ 80ºC Increase of Ni content → T M drops Substitution of Ti by Hf or Zr raises T M  (Ti+Hf/Zr)-rich ternary alloys Recently, study of Ni-rich ternary alloys High industrial interest (automotive, aerospace, …)

Activity in the framework of IIMEC in 2011

MaterialsMaterials Materials: Selected in TAMU Ni 50.3 Ti 34.7 Zr 15 15Zr (at%) Ni 50.3 Ti 29.7 Zr 20 20Zr Ni 50.3 Ti 34.7 Hf 15 15Hf Hot extruded (900ºC) Solution Heat Treatment: 900 o C, 1h + WQ (SHT)

Collaboration plan “Macroscopic” characterization of functional properties DSC Thermal cycling under stress Thermal treatments to improve functional properties Alper’s PhD Microstructural characterization TEM, HRTEM EDX Most of observations performed during Alper’s stay Afterwards: Analysis of results

General Results VERY FRUITFUL ACTIVITY:  Education: Intense immersion in practical TEM/HRTEM work (preparation of samples and observations)  Personal life: Stay in a country with different culture  Collaboration: Strong impulse to TAMU-UIB collaboration  Scientific: Good results suitable for several publications

Scientific Results As extruded and Solution Heat Treated state Low T M temperatures and poor reproducibility Thermal treatments to improve the alloy performance 20Zr 15Hf

Scientific Results 20Zr DSC results

Scientific Results 15Hf DSC results

Scientific Results 20Zr Furnace cooling from 700ºC to 100ºC in 48h

Scientific Results 15Hf SHAPE MEMORY EFFECT 10h at 550ºC ~ 2.5%

Scientific Results Microstructural observations in aged samples Precipitation of a new phase Ni-rich NiTi  Ni 4 Ti 3 or Ni 3 Ti Not in ternary alloys

15Zr 200h at 500ºC Austenite at RT Lenticular precipitates in austenitic matrix. ~ 20 nm Scientific Results TEM HRTEM

The precipitates show an enhanced contrast every three 011 planes and extra spots in the diffraction patterns. They are fully coherent with austenitic matrix. Scientific Results 15Zr 200h at 500ºC Austenite at RT

15Hf 10h at 450ºC Austenite at RT Nanometric precipitates (~5 nm) Scientific Results

20Zr 48h at 500ºC Scientific Results 15Hf 3h at 500ºC Precipitates in martensite

20Zr 700ºC-100ºC FC Long precipitates O(100 nm) Scientific Results

EDX Microanalysis Scientific Results 15Hf 10h at 600ºC 20Zr 700ºC-100ºC FC Precipitates are richer in Hf/Zr and poorer in Ti, and a bit richer in Ni.

Twinning modes of B19’ martensite in samples with precipitates Scientific Results

Twinning modes of B19’ martensite in samples with precipitates Scientific Results (011) B19’ Type I twinning Twin plane || intervariant boundary (001) B19’ compound twinning (internal twins - LIS) Same twinning modes and boundaries as reported in literature for Ni-Ti-Hf alloys {111} and {113}-type intervariant boundaries

Intervariant boundaries Scientific Results {111} or {113}-type boundaries quite irregular (011) Perfect (011) boundaries || twin plane

Intervariant boundaries Scientific Results {111} or {113}-type boundaries quite irregular (011) Perfect (011) boundaries || twin plane

Structural model of the precipitate new phase Scientific Results

Benefits received from IIMEC Benefits in Alper’s education and personal life The summer stay provided a strong impulse to TAMU-UIB collaboration Several good publications envisaged Creation of a good scientific common background for possible future applications of research projects in International Programs (NSF, EU, …)

Thanks for your attention!!!

Scientific Results 15Hf SHAPE MEMORY EFFECT SHT ~ 3.5%

Scientific Results 20Zr Af temperature vs ageing time

Scientific Results 15Hf Af temperature vs ageing time