Liquid metal infiltrated interpenetrating composites based on bulk metallic glass - processing, characterization and modeling

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Metal matrix composites (MMCs) with reinforcements of bulk metallic glass (BMG) have great potential in terms of elastic-specific energy absorption capacity, hardness and strength. The susceptibility to brittle fracture and low toughness is a disadvantage of BMG. In this regard, the potential of BMG-foams could already be shown, as the plasticity under compressive loads is significantly increased due to the collapse of the foam webs. BMG-foams have already been successfully produced in the past. The combination of a BMG-foam with a metal matrix to form a MMC has not taken place so far. The aim of the project is therefore the investigation of MMCs with a three-dimensional, interpenetrating structure made of BMG. A good reinforcing effect can be achieved, by successfully embedding BMG into a metallic matrix. The present application involves the processing and materials characterization of MMCs with a 3-dimensional BMG interpenetrating structure. Due to the load-bearing function of BMG, the interpenetrating structure is expected to improve the mechanical properties of the composite compared to conventional 0- (particle) or 1- and 2- dimensional reinforcements (ribbons). Higher mechanical properties can be achieved especially under compressive loads, because the collapse of the foam webs leads to higher plasticity. The BMG-foam processing planned in the present application is realized by means of die hot pressing of BMG and salt particles. The latter being washed out in a subsequent process step. The open-pore BMG-foam produced in this way is infiltrated by means of gas pressure infiltration with aluminum afterwards. Preliminary work of the applicant has shown that the BMG Ni60Nb20Ta20 has a relatively high crystallization temperature (969 K) coupled with very good glass-forming tendency and high hardness and strength. The crystallization temperature is thus significantly higher than the melting temperature of the eutectic aluminum alloy AlSi12, which enables a melt-metallurgical processing of an MMC based on a 3-dimensional network of Ni60Nb20Ta20. Process parameters of the infiltration are to be varied and the process-structure-property relationships are to be investigated by means of mechanical and microstructural characterization methods. In addition to the 2- and 3-dimensional microstructure analysis, the methods used include the determination of the elastic properties by means of UPS, mechanical tests with (in-situ) and without (ex-situ) simultaneous analysis of the damage behavior. Furthermore, the thermal expansion coefficient and the influence of thermal-mechanical loads on the structure and properties of the composite are to be determined.