Abstract
Powder metallurgy (P/M) material subjected to plastic deformation results into densification, however the extended deformation would not only enhance the densification also supplements the strain hardening. Unlike fully dense material that would only undergo strain hardening while plastic deformation, the P/M material leads to pore closure as well; this phenomenon complicates the work hardening mechanism. The present study revealed that both strain and density configures strengthening of P/M preform, which respectively termed as matrix and geometric work hardening. An attempt has been made to delineate some aspects of work hardening behaviour with the influence of different aspect ratios of sintered and cold deformed copper alloy preforms. The preforms were initially prepared through conventional P/M route and finally subjected to cold upsetting under dry friction condition. A statistical analysis has also been introduced to study the quantitative impact of strain and density in the presence of aspect ratio on work hardening rate characteristics.
Highlights
Cold forging on sintered powder preforms would undergo both ductile fracture and strain hardening mechanisms, which in particular demonstrate the feasibility of forming processes
A best curve fitting technique is applied, as a consequence a third order polynomial curve with regression co-efficient of almost unity is observed. This reveals that stress behaves against strain in three different mechanisms; at initial stage, this falls between nil strain to 0.06 strain, its stress respectively zero to 262 MPa, relatively peak rise in stress
Empirical relationship has been obtained for flow stress against strain and density, in which the effect of aspect ratio is embedded
Summary
Cold forging on sintered powder preforms would undergo both ductile fracture and strain hardening mechanisms, which in particular demonstrate the feasibility of forming processes. These mechanisms subsequently results in promoting densification and mechanical properties in the final products[1,2]. It was found that strain hardening could happen in the P/M material by means of matrix as well as geometric[11]; various attempts had been made to explain this behavior with different compositions, preform geometries and friction conditions as major influencing parameter[12,13,14,15,16]. In the present investigation an attempt has been made to rationalize this behaviour by considering copper alloy preform subjected to secondary deformation such as cold upsetting under dry friction condition. Using statistical analysis the contribution of material parameters such as relative density and axial strain with the influence of various aspect ratios on work hardening rate has been quantified
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