J.W. XianM.A.A. Mohd SallehS.A. BelyakovT.C. SuG. ZengK. NogitaH. YasudaC.M. GourlayTE-CHENG SU2020-09-022020-09-02201809669795https://scholars.lib.ntu.edu.tw/handle/123456789/513587https://www.scopus.com/inward/record.uri?eid=2-s2.0-85052514021&doi=10.1016%2fj.intermet.2018.08.002&partnerID=40&md5=8feb86952964a553d15fb6d267bfaa6fThe influence of Ni on the size and twinning of primary Cu6Sn5 crystals in Sn-0.7Cu-0.05Ni and Sn-xCu (x = 0.7, 0.9, 1.1) (mass%) solder joints is studied using synchrotron radiography and SEM-based EBSD. It is shown that the Ni addition does not cause significant refinement of primary Cu6Sn5 if the alloy is fully melted. However, for peak temperatures ≤250 °C relevant to industrial soldering, primary Cu6Sn5 are not completely melted in Sn-0.7Cu-0.05Ni and there are 10–100 times more numerous and smaller crystals than in Sn-0.7Cu. X-shaped Cu6Sn5 crystals with an angle of ∼70° commonly formed in Sn-0.7Cu-0.05Ni/Cu joints and are shown to be penetration twins. This type of growth twinning was only found in partially melted samples, both in Sn-0.7Cu-0.05Ni/Cu joints and binary Sn-1.1Cu alloy. The frequency of twinned crystals was significantly higher in Ni-containing solders. The results are discussed in terms of the influence of Ni on the Cu6Sn5 liquidus slope and on the lattice parameters of (Cu,Ni)6Sn5. © 2018 Elsevier LtdA. Intermetallics; B. Twinning; C. Crystal growth; F. Electron backscatter diffraction; JoiningBinary alloys; Joining; Lead-free solders; Nickel; Soldering; Ternary alloys; Tin alloys; Twinning; Cu alloy; Electron back scatter diffraction; Liquidus; Ni additions; Peak temperatures; Sn-0.7cu; Solder joints; Twinned crystals; Copper alloysjournal article10.1016/j.intermet.2018.08.0022-s2.0-85052514021