Influence of titanium solute additions on the microstructural and mechanical behaviours of Ni-B alloys
Physics and Engineering physics,Obafemi Awolowo University
The study prepared seven ternary Ni-B-Ti alloys with varying compositions of titanium and one binary Ni-B alloy (control sample). It also determined the solidification path and phase formation of the alloys, their microstructures and their mechanical properties. This was with a view to determining the effect of varying amount of titanium on the microstructure and some mechanical properties of the Ni-B system. The components of the alloys were pure Ni, binary Ni-B containing 18.3wt%B and pure Ti.The components of each alloy were accurately weighed and then melted using an electric furnace. The samples were quenched in air after melting. Differential Thermal Analyzer (DTA) was used to study the solidification path and phase formation of the alloys. The heating and cooling rates ranged from 10-20oC/min. Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-ray Analyzer (EDXA) and Optical Microscope (OM) were used to characterise the structures of the alloys. The sample for SEM and OM investigations were polished, then slightly etched with an etchant consisting of 5g FeCl3+10ml HCl dissolved in 50ml H2O.Instron machine was used to measure the compressive strength of the alloys while the hardness values of the alloys were measured with a micro-hardness tester on the Vickers and Rockwell-C scale. Microscopic and thermal investigations of the alloys revealed the presence of two major primary phases [Ni(α), τ] and other binary and ternary eutectic structures. Microsegregation was not observed in the quenched alloys due to their very high solidification rates. Upon subjection to slow cooling, the microstructures of the alloys becomes complex due to solid-state reactions and large undercoolings in the alloys. The addition of titanium to the Ni-B system led to a shift in microstructure of the alloys from the hypoeutectic to the hypereutectic region during slow cooling. Solid state (eutectoid) transformation of the τ phase was observed in alloys with low titanium contents. But such transformation was not observed for alloys with high titanium contents. The hardness values and Stiffness values of the Ni-B-Ti matrix increased with increase in titanium contents. The study concluded that Ni-B-Ti alloys which were suitable as coating materials to solve wear and abrasive problems in the engineering industries could also be applied to make the materials harder and stiffer.
Titanium Solute, Microstructural, Mechanical behaviours, Ni-B Alloys, Engineering industries
Zeblon,E.M.(2016). Influence of titanium solute additions on the microstructural and mechanical behaviours of Ni-B alloys. Obafemi Awolowo University