The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles r...The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles rich in chromium, manganese and silicon precipitate during aging, and thereby increase the hardness and strength of the alloy. The shape recovery ratio can be remarkably improved by aging and a maximum value can be obtained at 1223 K, which is 68% higher than that of the specimen in solid solution state. When the aging temperature is below 1223 K, the amount of second phase particles increases as the aging temperature increases. The size of austenite grain increases with increasing aging temperature. When the temperature is over 1223 K, the second phase particles can not precipitate. The lack of second phase particles and the increase of grain size make the hardness and shape recovery ratio drastically decrease, when the temperature is over 1223 K.展开更多
This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5, 10, and 20 wt.% B_(4)C with bimodal sizes under different loadings(10-80 N) at various sl...This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5, 10, and 20 wt.% B_(4)C with bimodal sizes under different loadings(10-80 N) at various sliding speeds(0.1-1 m/s) via the pin-on-disc configuration.Microhardness evaluations showed that when the distribution of B_(4)C particles was uniform the hardness of the composites increased by enhancing the reinforcement content. The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content. For this purpose, wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses. The determined wear mechanisms were abrasion, oxidation, delamination, adhesion, and plastic deformation as a result of thermal softening and melting. The wear evaluations revealed that the composites containing 5 and 10 wt.% B_(4)C had a significantly higher wear resistance in all the conditions. However, 20 wt.% B_(4)C/AZ31 composite had a lower resistance at high sliding speeds(0.5-1 m/s) and high loadings(40-80 N) in comparison with the unreinforced alloy. The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear.展开更多
Mg-based alloys are potential candidate materials for a fabrication of lightweight boron carbide based composites through a reactive melt infiltration approach. In this paper, the effect of a mechanical purification o...Mg-based alloys are potential candidate materials for a fabrication of lightweight boron carbide based composites through a reactive melt infiltration approach. In this paper, the effect of a mechanical purification of molten AZ91 alloy’s surface on its wettability with polycrystalline B_(4)C is experimentally evaluated for the first time. For this purpose, sessile drop experiments were performed under the same operating conditions(700℃/5 min;Ar atmosphere), by using both the classical contact heating(CH) and the improved capillary purification(CP) procedure. It was found that the evolution of contact angle values was strongly influenced by the applied procedure. In particular, by using the classical CH procedure, the presence of a native oxide layer on the metal surface hinders the observations of melting process, resulting in a misleading conclusion that the system is non-wettable. Contrarily, during the wetting test performed by applying the CP procedure, the surface oxide layer was mechanically removed by squeezing the molten AZ91 alloy through a capillary. Accordingly, the oxide-free AZ91 drop with a regular and spherical shape was successfully obtained and dispensed on the B_(4)C substrate. A reliable contact angle value of θ =83° was measured at the AZ91/B_(4)C triple line at 700 ℃, which in turn proves that B_(4)C is wetted by the liquid AZ91 alloy. In contradiction to the literature, these good wetting conditions were assisted by a non-reactive wetting mechanism occurring at the AZ91/B_(4)C interface. To succeed in the fabrication of AZ91/B_(4)C composites by liquid metal infiltration, such experimental observations make it reasonable to expect a spontaneous infiltration process exclusively driven by capillarity, which in turn increases the efficiency of the process by the absence of reaction products that could be a potentially detrimental factor.展开更多
High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Amon...High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.展开更多
Comparisons of particle’s thermal behavior between Fe base alloy and boron carbide in plasma transferred arc (PTA) space was made based on theoretical evaluation results in this article. It was found that most of t...Comparisons of particle’s thermal behavior between Fe base alloy and boron carbide in plasma transferred arc (PTA) space was made based on theoretical evaluation results in this article. It was found that most of the Fe base particles would be fully melted while they transporting through the central plasma field with 200 A surfacing currents. And the particles with a diameter less than 0.5×10 -4 m might be fully evaporated. However, for the boron carbide (B 4C) particles, only the one with a diameter less than 0.5×10 -4 m could be melted in the same PTA space. Most of B 4C particles are only preheated at its solid state when they were fed through the central field of PTA plasma when the surfacing current is equal to or less than 200 A . When the arc current was smaller than100 A , only the particles smaller than 0.5×10 -4 m could be melted in the PTA space for the Fe base alloy. Almost none of the discussed B 4C particles could be melted in the 100 A PTA space.展开更多
文摘The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles rich in chromium, manganese and silicon precipitate during aging, and thereby increase the hardness and strength of the alloy. The shape recovery ratio can be remarkably improved by aging and a maximum value can be obtained at 1223 K, which is 68% higher than that of the specimen in solid solution state. When the aging temperature is below 1223 K, the amount of second phase particles increases as the aging temperature increases. The size of austenite grain increases with increasing aging temperature. When the temperature is over 1223 K, the second phase particles can not precipitate. The lack of second phase particles and the increase of grain size make the hardness and shape recovery ratio drastically decrease, when the temperature is over 1223 K.
文摘This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5, 10, and 20 wt.% B_(4)C with bimodal sizes under different loadings(10-80 N) at various sliding speeds(0.1-1 m/s) via the pin-on-disc configuration.Microhardness evaluations showed that when the distribution of B_(4)C particles was uniform the hardness of the composites increased by enhancing the reinforcement content. The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content. For this purpose, wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses. The determined wear mechanisms were abrasion, oxidation, delamination, adhesion, and plastic deformation as a result of thermal softening and melting. The wear evaluations revealed that the composites containing 5 and 10 wt.% B_(4)C had a significantly higher wear resistance in all the conditions. However, 20 wt.% B_(4)C/AZ31 composite had a lower resistance at high sliding speeds(0.5-1 m/s) and high loadings(40-80 N) in comparison with the unreinforced alloy. The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear.
基金the financial support given by the National Science Centre (NCN) in Poland,under the project MINIATURA 2, No. 2018/02/X/ST8/03044 in2019–2020。
文摘Mg-based alloys are potential candidate materials for a fabrication of lightweight boron carbide based composites through a reactive melt infiltration approach. In this paper, the effect of a mechanical purification of molten AZ91 alloy’s surface on its wettability with polycrystalline B_(4)C is experimentally evaluated for the first time. For this purpose, sessile drop experiments were performed under the same operating conditions(700℃/5 min;Ar atmosphere), by using both the classical contact heating(CH) and the improved capillary purification(CP) procedure. It was found that the evolution of contact angle values was strongly influenced by the applied procedure. In particular, by using the classical CH procedure, the presence of a native oxide layer on the metal surface hinders the observations of melting process, resulting in a misleading conclusion that the system is non-wettable. Contrarily, during the wetting test performed by applying the CP procedure, the surface oxide layer was mechanically removed by squeezing the molten AZ91 alloy through a capillary. Accordingly, the oxide-free AZ91 drop with a regular and spherical shape was successfully obtained and dispensed on the B_(4)C substrate. A reliable contact angle value of θ =83° was measured at the AZ91/B_(4)C triple line at 700 ℃, which in turn proves that B_(4)C is wetted by the liquid AZ91 alloy. In contradiction to the literature, these good wetting conditions were assisted by a non-reactive wetting mechanism occurring at the AZ91/B_(4)C interface. To succeed in the fabrication of AZ91/B_(4)C composites by liquid metal infiltration, such experimental observations make it reasonable to expect a spontaneous infiltration process exclusively driven by capillarity, which in turn increases the efficiency of the process by the absence of reaction products that could be a potentially detrimental factor.
基金Financial assistance from Armament research board,New Delhi,India
文摘High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.
文摘Comparisons of particle’s thermal behavior between Fe base alloy and boron carbide in plasma transferred arc (PTA) space was made based on theoretical evaluation results in this article. It was found that most of the Fe base particles would be fully melted while they transporting through the central plasma field with 200 A surfacing currents. And the particles with a diameter less than 0.5×10 -4 m might be fully evaporated. However, for the boron carbide (B 4C) particles, only the one with a diameter less than 0.5×10 -4 m could be melted in the same PTA space. Most of B 4C particles are only preheated at its solid state when they were fed through the central field of PTA plasma when the surfacing current is equal to or less than 200 A . When the arc current was smaller than100 A , only the particles smaller than 0.5×10 -4 m could be melted in the PTA space for the Fe base alloy. Almost none of the discussed B 4C particles could be melted in the 100 A PTA space.
