Transient liquid phase (TLP) bonding of Cu substrates was conducted with interlayer systems with the stacking sequences Ag-Sn-Ag (samples A), Ni-Sn-Ni (samples B), and combined Ag-Sn-Ni (samples C). Because of the low mismatch of the coefficients of thermal expansion, characteristics of the TLP process and mechanical and thermal behavior of TLP-bonded samples could be investigated without interference from thermally induced residual stresses. An ideal process temperature of 300°C, at which the number of pores was lowest, was identified for all three layer systems. It was verified experimentally that formation of pores resulted from volume contraction during isothermal solidification of liquid Sn into intermetallic compounds (IMC). Temperature and interlayer-dependent growth characteristics of IMC accounted for the increasing size and number of defects with increasing process temperature and for different defect positions. The shear strength was measured to be 60.4 MPa, 27.4 MPa, and 40.7 MPa for samples A, B, and C, respectively, and ductile fracture features were observed for Ag 3 Sn IMC compared with the purely brittle behavior of Ni 3 Sn 4 IMC. Excellent thermal stability for all three layer systems was confirmed during long-term annealing at 200°C for up to 1200 h, whereas at 300°C the microstructure was driven toward Ag-Sn solid solution, accompanied by Cu diffusion from the substrate along grain boundaries and Cu 3 Sn IMC formation (A), and toward Ni-rich IMC phases (B). Combined IMC interlayers (C) tended to be transformed into Ni-based IMC when held at 300°C; intermixing into (Ni,Cu) 3 Sn was accompanied by pore formation.

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The stress-induced fcc-austenite to hcp-martensite transformation in the iron based shape memory alloy (SMA) Fe-17Mn-5Si-10Cr-4Ni with and without VC precipitates is investigated by in-situ neutron diffraction measurements upon uniaxial loading and unloading. Based on experimentally derived elastic moduli the critical resolved shear stress (CRSS) for the fcc to hcp phase transformation was calculated. VC precipitates promote the martensite transformation by shifting the CRSS from 152 MPa to 85 MPa. A nearly perfect plastic behavior is found for the (220) grains with a high Schmid factor of 0.47. While (220), (111) and (200) oriented grains exhibit a phase transformation, (311) grains plastically deform solely by slip. During plastic deformation a load redistribution from soft behaving (220) grains to hard behaving (200) orientated grains takes place. The presence of VC precipitates leads to a broadening of the stress interval at which a martensite transformation is induced. This is explained by spatially heterogeneously distributed martensite transformation temperatures which are caused by VC precipitates. The microstructural reason for pseudo-elasticity is found to be a combination of back transformation from hcp to fcc and a reversible motion of Shockley partial dislocations.

The creep and stress relaxation behavior of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (wt-%) shape memory alloy at low homologous temperatures (-45°C