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Cracks in interfaces and around their junctions in WC/Co composite

Postek E., Sadowski T.

Engineering Transactions

2016

Vol. 64, iss. 4

589--596

WC/Co ceramic metal-matrix composites are characterized by very high mechanical properties that allow for application of the composites mostly in production of different types of cutting tools. By combining in a composite structure a phase of brittle hard wolfram carbide (WC) grains with a metallic interface of cobalt (Co) that exhibits plastic properties, a geometrically complex microstructure with significantly different mechanical properties of the combined phases is created, see Fig. 1a. The presence of the elastic-plastic interface material, i.e. Co binder, in the composite structure is the reason for initiation of technological defects – mainly material porosity. During material loading pores start to coalesce and finally one can observe creation of microcracks system distributed along interfaces. The aim of the paper is to show the previously formulated model [1, 2] of the polycrystalline composite to be extended towards cracks development around the junctions of the interfaces. The obtained numerical results indicate that in the junctions high stress concentrations were observed, which leads to crack initiation and its further unstable propagation, and finally the composite failure. Results indicate that the first crack appears close to the junction and that the load carrying capacity of the sample is overestimated if a crack model in the interfaces is not assumed.

Napawanie elektryczne oporowe warstw niklowych i kobaltowych z dodatkiem węglika wolframu.

Bartnik Z.

Inżynieria Materiałowa

1999

R. XX, nr 5

362-364

Metodą napawania elektrycznego oporowego wykonano cienkie warstwy na podłożu stalowym o grubości 2,5 mm. Użyto jako materiału na warstwy mieszaniny proszku stopowego na osnowie niklu i węglika wolframu oraz mieszaniny proszku kobaltu i węglika wolframu. Podczas napawania oporowego rejestrowano w sposób ciągły parametry elektryczne procesu. Dokonano obserwacji mikroskopowych wraz z mikroanalizą punktową z obszaru podłoże - granica połączenia - warstwa napawana. Mierzono twardość warstw i przeprowadzono próby zginania warstw do uzyskania równoległości ramion.

Thin layers were created on the surface of 2,5 mm steel substrate by means of electrical resistance pad welding. The layers were made of mixed nickel alloy powder with tungsten carbide and cobalt powder with tungsten carbide. During electrical resistance welding the electrical parameters of the process were recorded. Microscopical observations and microanalysis of the area between foundation and the border of the joint were carried out as well. On the basis of hardness measurement and bend test the selected layer properties were established.