Microstructural instability in coated single crystal superalloys

作者：Reid M^*; Pomeroy MJ; Robinson JS

来源：Journal of Materials Processing Technology, 2004, 153: 660-665.

DOI：10.1016/j.jmatprotec.2004.04.132

• superalloys
• diffusion
• platinum aluminide

Specimens of CMSX-4 and CMSX-10 alloys have been platinum aluminised to give a single phase (Ni,Pt)AI coating and a two phase PtAl2-(Ni,Pt)Al coating, respectively. Specimens of the coated alloys were exposed in an oxidising environment for 188, 350 and 750 h at a temperature of 1100 degreesC. Specimens were then sectioned, polished and examined using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). Decreases in nickel activity and increases in aluminium activity occurred within the substrate close to the coating/alloy interface. These effects resulted in precipitation of additional gamma' in the alloy, which caused rafting of the gamma' and encapsulation of needle-like sigma phase in gamma'. The development of these needle-like sigma phases beneath the diffusion layer in the CMSX-10 alloy at 1100 degreesC is significant, such that they extend to a depth of 0.2 mm. In addition, they cause failure at the coating/substrate interface in the case of the CMSX-10 alloy. For the CMSX-4 alloy, equilibration effects remote from the coating cause further precipitation of sigma phases in isolated cells in gamma' regions. The implications of these instabilities on superalloy properties are discussed.

• 出版日期2004-11-10