ABSTRACT
The effects of different boron (B) additions from 0 to 0.5 wt.% on the microstructure and properties of Fe-Mo-Cu-Ni-xB-C powder metallurgy (PM) steels were investigated in this work. The results indicated that the ferrite phase quantity decreased and disappeared, Ni/Cu became more homogeneous, and M2B phase formed, with the addition of B. The density and hardness of the sintered steels monotonously increased with increasing B content, whereas the tensile strength and impact toughness first increased and then decreased. The tensile strength of the steels reached a maximum value of 1097 MPa at a 0.2% B content, whereas the impact toughness reached a maximum value of 25.7 J/cm2 at a 0.1% B content and then sharply decreased when the B content exceeded 0.2%. Frictional wear experiments showed that the weight loss of the steels decreased with an increasing B content under low load conditions (100 N), and the lowest weight loss of 0.043 g occurred at a 0.2% B content. Under high load conditions (200 N), the 0.1% B content steel saw the lowest weight loss 0.075 g, exhibiting excellent wear resistance, but the abrasive resistance of the steels decreased with a further increase in the B content due to the germination of microcracks and large spalling caused by the high hardness and brittleness.
ABSTRACT
Fe-Cu-Co prealloyed powder is used for bonding metal of diamond tools. In order to obtain diamond tools with good mechanical properties by pressureless sintering, it is necessary to add Cu-Sn sintering aids. The substrate also has high corrosion resistance requirements, which is conducive to the chemical erosion of diamond tools. This paper mainly studies the effects of Cu-Sn on the corrosion behavior of pressureless sintered Fe-Cu-Co substrate. The results show that the linear contraction rate and relative density of pressureless sintered Fe-Cu-Co alloy at 875 °C reach their peak when the Cu-Sn content is 8 wt.%, 15.13% and 97.5%, respectively. The substrate is mainly composed of α-Fe and Cu-rich phases, and selective corrosion occurs during electrochemical corrosion; namely, α-Fe grains are more prone to corrosion than Cu-rich grains to form porous corrosion surfaces. With the increase in Cu-Sn addition, the volume fraction of the Cu-rich phase increases, the corrosion current density and the passive current density gradually decrease, and the corrosion resistance of the alloy is improved. The amount and integrity of anodic passive film on the Fe-Cu-Co surface increases with the increase in Cu-Sn addition. The oxygen content of the anodic passivation film is lower than that of the active corrosion products of the α-Fe phase, thus reducing the oxygen concentration gradient and slowing down the corrosion. The addition of Cu-Sn is conducive to improving the corrosion resistance of Fe-Cu-Co alloy as the substrate of diamond tools.
ABSTRACT
To regulate the electronic structure of Bi sites and enhance their intrinsic activity, metal Bi with abundant defects was constructed. The optimized sample displayed a higher selectivity (93.9% at -0.9 V) and a larger current density (-10 mA cm-2 at -1.0 V) towards electrocatalytic CO2 reduction to formate, which can be mainly attributed to abundant defect sites and the optimized electronic structure. The assembled Zn-CO2 batteries displayed a power density of 1.16 mW cm-2 and a cycling stability up to 22 h. This work deepens the research of Bi-based catalysts towards CO2 transformation and related energy devices.
ABSTRACT
The effects of one-step aging and double aging on the properties and microstructures of 7075 Al sheets were studied via mechanical property testing, scanning electron microscopy, and transmission electron microscopy. The results indicated that with continued one-step aging, the tensile and yield strengths of the Al sheets first increased rapidly with an increase in the treatment time to 8 h and then increased slightly with a further increase in the treatment time to 10 h. The tensile and yield strengths became constant after 16 h of treatment. The mechanical strength properties of the Al sheets peaked after 16 h of one-step aging. However, the double aging treatment provided better mechanical properties and working efficiency than the one-step aging treatment. The tensile strength and microhardness resulting from double aging were greater than those resulting from one-step aging by 5.87% and 8.71%, respectively. Herein, we quantified the contribution ofvarious strengthening mechanisms.
ABSTRACT
TiC-high Mn steel-bonded carbide with a cellular structure was designed and fabricated by powder metallurgy techniques using coarse and fine TiC particles as the hard phase. This preparation process of the alloy was designed carefully and optimized. The microstructure of the alloy was observed using a scanning electron microscope. The results show that there are two types of microstructures observed in this TiC steel-bonded carbide: the coarse-grained TiC structure and fine-grained TiC structure. The transverse rupture strength and impact toughness of the alloy reach maximum values 2231 MPa and 12.87 J/cm2, respectively, when the starting weight ratio of MP-A (containing coarse TiC particles) to MP-B (containing fine TiC particles) is 60:40. Hence, this study serves as a feasible and economical example to prepare a high-strength and high-toughness TiC-high Mn steel-bonded carbide with little production cost increase.
ABSTRACT
In the present work, the mechanical and tribological properties of carbon nanotube (CNT)-reinforced Cu matrix composites featuring 0-1.8 vol% CNTs prepared by spark plasma sintering under dry sliding and boundary lubrication conditions were investigated. The results of microstructure revealed that the bonding interface in Cu/CNT composites was very well established. Additionally, the addition of CNTs has a positive effect on improving the hardness and tensile strength of the composites, while the stress-strain response quasi-static tensile test confirms the same results. CNTs are proved to lead to certain self-lubrication. The addition of CNTs could result in decreased coefficient of friction (COF) and wear rates by reducing adhesive wear under dry sliding conditions, while the oil lubricating film was the major reason for decreased COF under boundary lubrication conditions.
