Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardnes...Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardness testing belong to the Palmquist crack system. The value of highest fracture toughness of MoSi 2+ZrO 2+SiC composite is 7.58?MPa·m 1/2 , which is nearly three times that of monolithic MoSi 2. This can be attributed to well distributed ZrO 2 and SiC particles along the boundaries of very fine MoSi 2 grains.展开更多
The grain size of AZ91 alloy was investigated in terms of the effects of cooling rate, superheat and steel gauze. It was found that rapid cooling rate and low superheat favoured the achievement of fine grain structure...The grain size of AZ91 alloy was investigated in terms of the effects of cooling rate, superheat and steel gauze. It was found that rapid cooling rate and low superheat favoured the achievement of fine grain structures. The gauze had a less profound effect on the grain size in AZ91 magnesium alloy than that in A356 aluminum alloy. The mechanisms by which these factors affect grain refinement of AZ91 have also been discussed.展开更多
The surface composition of low alloy steel after N_2^+ implantation was studied with X-ray photo-electron spectroscopy (XPS). The effect of the implantation on the mechanical hardness was evaluated by ultra-micro hard...The surface composition of low alloy steel after N_2^+ implantation was studied with X-ray photo-electron spectroscopy (XPS). The effect of the implantation on the mechanical hardness was evaluated by ultra-micro hardness indentation. Chemical characterisation of the surface indi- cated that a thin layer rich in N, C and Si was formed. It is shown that Fe played little role in the chemical composition and the structure of the modified surface. The mechanical hardness of N_2^+ implanted surface was 35-50 GPa compared with a value of 10 GPa for the untreated sample. It is thought that the high hardness observed on the surface and in the sub-surface was as a result of chemical modification to form a film of Si doped carbon nitride. There is strong evidence from the XPS and the nanoindentation studies that the bonding structure of the C-N in the near surface is essentially sp^3 types expected in crystalline C_3N_4. The value of nitrogen ion implantation as process for improving the wear resistance of low alloy steels is emphasized.展开更多
文摘Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardness testing belong to the Palmquist crack system. The value of highest fracture toughness of MoSi 2+ZrO 2+SiC composite is 7.58?MPa·m 1/2 , which is nearly three times that of monolithic MoSi 2. This can be attributed to well distributed ZrO 2 and SiC particles along the boundaries of very fine MoSi 2 grains.
文摘The grain size of AZ91 alloy was investigated in terms of the effects of cooling rate, superheat and steel gauze. It was found that rapid cooling rate and low superheat favoured the achievement of fine grain structures. The gauze had a less profound effect on the grain size in AZ91 magnesium alloy than that in A356 aluminum alloy. The mechanisms by which these factors affect grain refinement of AZ91 have also been discussed.
文摘The surface composition of low alloy steel after N_2^+ implantation was studied with X-ray photo-electron spectroscopy (XPS). The effect of the implantation on the mechanical hardness was evaluated by ultra-micro hardness indentation. Chemical characterisation of the surface indi- cated that a thin layer rich in N, C and Si was formed. It is shown that Fe played little role in the chemical composition and the structure of the modified surface. The mechanical hardness of N_2^+ implanted surface was 35-50 GPa compared with a value of 10 GPa for the untreated sample. It is thought that the high hardness observed on the surface and in the sub-surface was as a result of chemical modification to form a film of Si doped carbon nitride. There is strong evidence from the XPS and the nanoindentation studies that the bonding structure of the C-N in the near surface is essentially sp^3 types expected in crystalline C_3N_4. The value of nitrogen ion implantation as process for improving the wear resistance of low alloy steels is emphasized.
