Segmentation and shear localization when turning TiMMC (Titanium Metal Matrix Composites)

Titanium Metal Matrix Composite (TiMMC) is a new class of material, which has a high potential in industrial applications. The TiC ceramic particles in the titanium matrix improve its physical properties; however they also cause high abrasive wear of the cutting tool during machining. Machining TiMMC produces segmented chips which have been attributed to "plastic instability". However their cause and mechanism are not well studied for cutting experiments. The segmentations are characterized by Adiabatic Shear Bands (ASB). Extensive theoretical and experimental studies toward an improved understanding of the shear localization started since the early seventies. ASB are observed to occur in many materials when subjected to high strain, and high strain rates. Most studies of ASB were done for impact tests. Lately due to the advances in new imaging technology, ASB have been more thoroughly studied. Accordingly, Dynamic Recrystallization (DRX) seems to be a phenomenon preceding ABS, and it results in very small equiaxed grains. Furthermore super high strain rates have been identified in the shear zones. In ballistic experiments ASB have been identified as a precursor to fracture, which outlines the importance of this phenomenon. This paper focuses on the understanding of the segmentation phenomenon and the ASB when machining TiMMC, while observing the effects of the TiC particles on the ASB.