The effect of quenching temperature from 900 to 1050°C on the microstructures, mechanical properties and abrasion resistance of modified high born cast steel containing 0·3 wt-%C and 3·0 wt-%B was studied by optical microscopy, scanning electron microscopy, X-ray diffraction analysis, tensile tester, impact tester, hardness tester and abrasion tester. Quenching at 900°C resulted in structures containing a small amount of pearlite. The existence of pearlite led to poor hardness and wear resistance of modified high born cast steel. Quenching at temperatures between 900 and 950°C resulted in the decrease in pearlite and the increase in hardness and abrasion resistance in comparison with 900°C quenching. The metallic matrix all transformed into the martensite quenching at 1000°C; the modified high born cast steel had high hardness, tensile strength, impact toughness and excellent abrasion resistance. The hardness, tensile strength and impact toughness of modified high born cast steel had no obvious change quenching over 1000°C. The increase in quenching temperature also led to the transformation of boride from continuous shape to isolated shape and promoted the coarsening of boride.

Using the finite-time thermodynamics, an irreversible cycle model of the Stirling refrigeration-cycle, using a ferroelectric material as the working substance, is established. Several irreversibilities due to thermal resistances between the working substance and the heat reservoirs, regenerative losses in two regenerative processes are taken into account. The influence of these irreversible losses on the performance of the ferroelectric Stirling refrigeration-cycleis analyzed. The thermoeconomic optimization for ferroelectric Stirling refrigeration-cycle is reported. The cooling load for the refrigerator per unit total cost is proposed as objective functions for the optimization. The optimum performance parameters which maximize the objective functions are investigated. Since the optimization technique consists of both investment and energy consumption costs, the obtained results are more general and realistic.

In this paper, a reliable design strategy, capable of optimally picking out the geometrical parameters of the 3-RRR planar parallel manipulators, is presented. The distribution charts for singular loci and usable workspace shape are obtained in the non-dimensional design space. Based on the singularity-free workspace and good force transition capacity, the optimum kinematic parameters are determined by means of the global conditioning index. An example shows that the strategy is useful for realizing the singularity-free workspace optimally.

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