Effect of solidification cooling rate on microstructure and tribology characteristics of Zn-4Si alloy

The main objective of this work was to modify the microstructure and enhance the tribological properties of a new Zn-4Si al-loy through a high solidification cooling rate(SCR).According to the results,by increasing the SCR from 2.0 to 59.5℃/s the average size of primary Si particles and that of the grains reduced from 76.1 and 3780μm to less than about 14.6 and 460μm,respectively.Augment-ing the SCR also enhanced the microstructural homogeneity,decreased the porosity content(by 50%),and increased the matrix hardness(by 36%).These microstructural changes enhanced the tribological behavior.For instance,under the applied pressure of 0.5 MPa,an in-crease in the SCR from 2.0 to 59.5℃/s decreased the wear rate and the average friction coefficient of the alloy by 57%and 23%,respect-ively.The wear mechanism was also changed from the severe delamination,adhesion,and abrasion in the slowly-cooled alloy to the mild tribolayer delamination/abrasion in the high-cooling-rate-solidified sample.

Mechanical properties of Al-15Mg_(2)Si composites prepared under different solidification cooling rates

The effect of different cooling rates(2.7,5.5,17.1,and 57.5℃/s)on the solidification parameters,microstructure,and mechanical properties of Al-15Mg_(2)Si composites was studied.The results showed that a high cooling rate refined the Mg_(2)Si particles and changed their morphology to more compacted forms with less microcracking tendency.The average radius and fraction of primary Mg_(2)Si particles decreased from 20μm and 13.5%to about 10μm and 7.3%,respectively,as the cooling rate increased from 2.7 to 57.5℃/s.Increasing the cooling rate also improved the distribution of microconstituents and decreased the grain size and volume fraction of micropores.The mechanical properties results revealed that augmenting the cooling rate from 2.7 to about 57.5℃/s increased the hardness and quality index by 25%and245%,respectively.The high cooling rate also changed the fracture mechanism from a brittle-dominated mode to a high-energy ductile mode comprising extensive dimpled zones.

Size distribution of inclusions in 12%Cr stainless steel with a wide range of solidification cooling rates

The effect of solidification cooling rate on the size and distribution of inclusions in 12%Cr stainless steel was investigated. A wide range of solidification cooling rates（from 0.05 to 106 K·s^-1） was achieved using various solidification processes, including conventional casting, laser remelting, and melt spinning. The size and distribution of inclusions in the steel were observed and statistically collected. For comparison, mathematical models were used to calculate the sizes of inclusions at different solidification cooling rates. Both the statistical size determined from observations and that predicted from calculations tended to decrease with increasing cooling rate; however, the experimental and calculated results did not agree well with each other at excessively high or low cooling rate. The reasons for this discrepancy were theoretically analyzed. For the size distribution of inclusions, the effect of cooling rate on the number densities of large-sized（〉 2 μm） inclusions and small-sized（≤ 2 μm） inclusions were distinct. The number density of inclusions larger than 1 μm was not affected when the cooing rate was less than or equal to 6 K·s^-1 because inclusion precipitation was suppressed by the increased cooling rate.

Phase Morphology Evolution in AISI301 Austenite Stainless Steel under Different Cooling Rates

Quenching experiments were performed at different cooling rates under non-directional solidification by differential thermal analysis, and the morphologic variation of primary phase, phase transition temperature and hardness change at the same quenching temperature were investigated. The experimental results show that, with the gradual decrease of the cooling rate from 25 K/min, the morphology of ferrite starts to transform experiencing the dendrite, radial pattern, Widmanstatten-like and wire-net. Sample starts to present the Widmanstatten-like microstructure at 10 K/min which does not exist at higher or lower cooling rates, and this microstructure is detrimental to the mechanical property. Except 10 K/min, the hardness decreases with decreasing cooling rate.

Effects of grain size on the corrosion resistance of pure magnesium by cooling rate-controlled solidification

The aim of this study was to investigate the effect of grain size on the corrosion resistance of pure magnesium developed for biomedical applications. High- purity magnesium samples with different grain size were prepared by the cooling rate- controlled solidification, Electrochemical and immersion tests were employed to measure the corrosion resistance of pure magnesium with different grain size. The electrochemical polarization curves indicated that the corrosion susceptibility increased as the grain size decrease. However, the electrochemical impedance spectroscopy （EIS） and immersion tests indicated that the corrosion resistance of pure magnesium is improved as the grain size decreases. The improvement in the corrosion resistance is attributed to refine grain can produce more uniform and density film on the surface of sample.