Effects of HfB2 and HfN Additions on the Microstructures and Mechanical Properties of TiB2-Based Ceramic Tool Materials
The effects of HfB2 and HfN additions on the microstructures and mechanical properties of TiB2-based ceramic tool materials were investigated. The results showed that the HfB2 additive not only can inhibit the TiB2 grain growth but can also change the morphology of some TiB2 grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB2-HfB2 ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB2 and Ni. The decrease of the flexural strength and Vickers hardness of the TiB2-HfN ceramics was due to the increase of defects such as TiB2 coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB2 coarse grains. The toughening mechanisms of TiB2-HfB2 ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB2-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.
Wear behaviour of Al2O3/Ti(C,N) ceramic tool during turning process of martensitic stainless steel
Abstract In this paper, we prepared an Al2O3/Ti(C,N) ceramic tool with main components of Al2O3 (41%), TiN (33%) and TiC (17%), and studied its cutting characteristics of continuous turning 1Cr13 martensitic stainless steel, the cutting performance of Al2O3/Ti(C,N) ceramic tool and 1Cr13 workpiece surface roughness were analysed in different cutting speeds. In cutting speed 260 m min−1, cutting depth 0·1 mm, cutting feed 0·1 mm r−1, the tool gets the best tool life, and ensures a good surface quality. The scanning electron microscope and energy dispersive spectroscopy analysis of Al2O3/Ti(C,N) ceramic tool is performed after cutting, and the wear mechanism of tool is abrasive wear and adhesive wear in high cutting speed.
Shape and surface texture of molten droplets deposited on cold surfaces
When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.