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The microstructure and mechanical properties of Ni78Ag2P20 alloy

Ziewiec K., Dutkiewicz J., Ziewiec A., Kąc S.

Archives of Materials Science and Engineering

2007

Vol. 28, nr 11

657-660

Purpose: The aim of the work was to investigate the influence of silver as a modifying constituent on structure formation in Ni-P based glass forming matrix and to characterize mechanical properties of the alloys. Design/methodology/approach: Nickel-silver-phosphorus Ni78Ag2P20 alloy was produced using arc melting in argon protective atmosphere from commercial powders. The alloy was melt spun. The microstructure of the arc melted droplet is investigated in scanning electron microscope with EDS and micro-hardness tester and the melt spun ribbon is investigated using light microscope and transmission electron microscope. Then the mechanical properties are evaluated with use of micro-hardness measurements. Findings: A strong tendency for demixing of Ni-P-rich and Ag-rich liquids is observed leading to formation of the primary structure consisting of slightly hypo-eutectic Ni-P-rich regions and Ag rich regions. The melt spinning process produced the amorphous Ni-P and Ag-rich crystalline structure. The alloys hardness and elasticity modulus were characterized. The melt spun ribbons are slightly softer than the crystalline Ni-P regions. In case of the melt spun ribbons, a softening influence of silver was observed giving the lower hardness for Ni78Ag2P20 than Ni80P20. The alloy constituents in a bulk crystalline state present the higher values of elasticity modulus when compared to the melt spun ribbons. Research limitations/implications: It has been shown that the criterion of a high positive values of mixing enthalpies can be applied to design the materials that should separate before the solidification to form a hard glassy matrix/soft crystalline composite. The amorphization of the crystalline Ni-P-based alloys can lead to formation of more flexible materials with a lower elasticity modulus and lower hardness. Practical implications: The main limits for application of the glassy alloys are the high prices of the materials used for alloying and the low plasticity of the amorphous metals. Therefore, the work provides the alloy produced from a low-cost commercial purity precursors that are able to form a glassy matrix composite with a crystalline soft particles included. The future works on the development of the idea can lead to a successful manufacturing of a hard and ductile metallic composite parts. Originality/value: The work delivers a new information on possibility of amorphous/crystalline composite formation starting from Ni Ag P system. This includes the original microstructural and mechanical characteristics of the arc melt and melt spun alloy. The information could be used by researchers for future works on development of Ni-P based composites complementary to the electroless coatings.