Guoxing Liang

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.

Testing Method and Experimental Studies on Single Laser Pulse Energy

A new type of testing device is designed for energy of laser pulse in this paper. By using it, pulse energy of KJG-1YAG-400A laser welder can be measured. The calorific models have been established for the device, and the analysis of thermal loss has been finished. Running curves have been obtained between time and resistance after the device absorbing laser energy. After test data is amended, the relationship among single pulse of laser energy, pulse width and current has been revealed, which provided theoretical foundation and practical experience for the laser brazing process.

Experimental studies on gear-honing-tool with laser brazing film CBN

During the process of brazing cubic boron nitride (CBN) gear-honing-tool by Laser, cleaning of the gear-honing-tool and film plating CBN abrasive, and the thickness of brazing coating directly affect the quality and life of gear-honing-tool. In the paper, based on experiment the process of laser brazing CBN is summed up, the thickness interrelationship of brazing filler metal from beginning to end is obtained, the rule of laser faculas moving speed is studied on solder layer thickness and the radial change of gear tooth thickness. It is shown that the bonding among CBN, gear-honing-tool and solder can be realized by laser brazing. In order to improve quality of brazing, the moving speed of laser facula must be reduced along radial direction of gear honing tool. As to different size of CBN abrasive, the thickness of solder layer should be varied so that the bare rates of cutting edge can be ensured. The solder layer thickness should be controlled between 1.25 and 1.5 times of average size of abrasive grains. The thickness of solder layer depends on laser energy and soldering time that can be controlled by the moving speed of laser facula.