Plasticity at Multiple Length Scales in Metal–Ceramic Interface Fracture

Abstract

Measurements of local plasticity in fracture of Ni–sapphire interfaces exhibit deformation on several length scales. The deformation processes are manifest as morphology on the surface of the Ni side of the fracture surface that can be quantified with scanning probe microscopies. Four scales of deformation are observed: ligamentary bridging, crack tip blunting, slip step formation and nanometer scale roughness. The relative amount of energy dissipated in each mechanism varies with interface strength and density of precipitates. Since the most energy intensive processes, i.e. ligamentary bridging and crack tip blunting, are associated with nano precipitates, large variations in interface toughness will be related to extrinsic factors.

The Influence of Oxide Interphases on the Toughness of the Interface Between α‐Al2O3 and Ni(Al) Intermetallic

“…9), reveal that, Γ I ≈ 6 J/m 2 , independent of the relative proportions of γ and γ′ phases. This toughness is much lower than that for Ni/Al 2 O 3 interfaces, 2,18,20 and comparable to that for interfaces weakened by S segregation 7,19,20 …”

“…This increases to Γ I >300 J/m 2 for the γ‐Ni(Cr)/α‐Al 2 O 3 interface 2,18,20 . But decreases to 1–10 J/m 2 upon either S segregation or spinel formation 2,17,19 . It remains to establish the corresponding characteristics for intermetallic/oxide interfaces.…”

“…Basic assessments of the adhesion of metal/oxide interfaces have been motivated by their growing industrial importance. These assessments have revealed that intimately‐bonded interfaces are inherently adherent: 1–10 but degrade upon impurity segregation and reaction product formation 11–20 . For example, the Ni/Al 2 O 3 interface has toughness, Γ I >100 J/m 2 2,18 .…”

“…These assessments have revealed that intimately-bonded interfaces are inherently adherent: 1-10 but degrade upon impurity segregation and reaction product formation. [11][12][13][14][15][16][17][18][19][20] For example, the Ni/Al 2 O 3 interface has toughness, G I 4100 J/m 2 . 2,18 This increases to G I 4300 J/m 2 for the g-Ni(Cr)/a-Al 2 O 3 interface.…”

“…2,18,20 But decreases to 1-10 J/m 2 upon either S segregation or spinel formation. 2,17,19 It remains to establish the corresponding characteristics for intermetallic/oxide interfaces. The intent of the present article is to provide a preliminary assessment for the (nominal) g 0 -Ni 3 Al/Al 2 O 3 interface, which is important within thermal barrier systems used in gas turbines.…”