Tensile Strength of Ni₄₅Al₄₅Cr_7.5Ta_2.5‐Coated Sapphire Fibers

Abstract

Continuous single-crystal a-Al 2 O 3 fibers were coated with Ni 45 Al 45 Cr 7.5 Ta 2.5 (IP75) alloy by physical vapor deposition (PVD). The strength of the coated fibers was evaluated by tensile testing and compared with the strength of uncoated fibers. The effect of temperature during diffusion bonding as well as the presence of a BN interlayer deposited by chemical vapor deposition (CVD) on the fiber strength was studied. Fibers coated with IP75, but without a BN interlayer, retained 23% of their initial strength after the PVD process and fractured during heat treatment. Evidence for thermal stress induced twin formation is presented. Fibers coated with a BN interlayer retained their initial strength during the coating processes. However, only 13% of their initial strength could be retained after the heat treatment. Here, chemical reactions cause morphological changes of the fiber surface. These may act as stress concentration sites, resulting in the extensive strength reduction reported here. These data are important for formulating future strategies avoiding or minimizing strength degradation during production of intermetallic matrix composites.

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…Properties and further possible applications of IP75 were discussed in several more recent investigations [1047][1048][1049][1050][1051][1052]. NiAl-Ta-Cr IP75 coatings were produced by thermal spraying applying the HVOF (high-velocity oxygen fuel) technique [1047], and fiber composites consisting of single-crystal a-Al 2 O 3 fibers that were PVD-coated with IP75 and hotpressed in vacuum were tested with respect to their mechanical properties [1048,1049]. However, a thick amorphous layer formed at the interfaces where debonding occurred making this kind of composite material unsuitable for high-temperature applications [1048].…”

Boron nitride nanofibers by the electrospinning technique

“…25,26 As nanofibers do have the longest axial ratio among all nanoshapes, ceramic nanofibers do have wide and potential applications. [27][28][29] Consequently, some researchers have tried to produce hexagonal boron nitride nanofibers using complicated procedure. 30 As the reported chemical synthesizing methods of boron nitride are complicated, so controlling the final product to be in 1D shape is very difficult task.…”