Investigation of deformation characteristics of micropins fabricated using microextrusion

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions of the order of less than 1 mm. At this length scale the deformation of the workpiece is dominated by the so-called 'size effects', e.g. material properties and frictional behavior vary at small length scales. In recent extrusion experiments performed to produce sub-millimeter sized pins having a base diameter of 0.76 mm and an extruded diameter of 0.57 mm, certain interesting deformation characteristics were observed. When a workpiece with a relatively large grain size of 211 μm was used, the billet tended to deform inhomogenously, and the extruded pins showed a tendency to curve. This phenomenon was not seen when workpieces with a smaller grain size of 32 μm were used. It is believed that the relative size and orientation of the large grains in the 211 μm grain size sample are responsible for this behavior and the aim of this paper is to investigate this phenomenon. Microindentation tests were performed on micropins extruded from workpieces of both grain sizes to obtain a measure of the distribution of induced strain. The results obtained from this analysis show that the deformation characteristics of the extruded pins are dominated by the size and location of specific grains leading to a non-uniform distribution of plastic strain and measured hardness.