An evaluation of steels subjected to rock bolt SCC conditions

In order to understand the metallurgical influences on rock bolt stress corrosion cracking (SCC), an evaluation has been carried out of a range of steels subjected to the conditions previously identified as producing laboratory SCC similar to that observed for rock bolts in service. The approach has been to use the linearly increasing stress test for samples exposed to a dilute pH 2.1-sulphate solution, as per our prior studies. SCC was evaluated from the decrease in tensile strength, ductility and fractography as revealed by scanning electron microscopy observation. A range of SCC susceptibilities was observed.     

Role of friction stir processing parameters on microstructure and microhardness of boron carbide particulate reinforced copper surface composites

Friction stir processing (FSP) was applied to fabricate boron carbide (B₄C) particulate reinforced copper surface composites. The effect of FSP parameters such as tool rotational speed, processing speed and groove width on microstructure and microhardness was investigated. A groove was contrived on the 6 mm thick copper plates and packed with B₄C particles. FSP was carried out using five various tool rotational speeds, processing speeds and groove widths. Optical and scanning electron microscopies were employed to study the microstructure of the fabricated surface composites. The results indicated that the selected FSP parameters significantly influenced the area of surface composite, distribution of B₄C particles and microhardness of the surface composites. Higher tool rotational speed and lower processing speed produced an excellent distribution of B₄C particles and higher area of surface composite due to higher frictional heat, increased stirring and material tranportation. The B₄C particles were bonded well to the copper matrix and refined the grains of copper due to the pinning effect of B₄C particles. B₄C particles retained the original size and morphology because of its small size and minimum sharp corners in the morphology.     

Modeling of grain refinement in aluminum and copper subjected to cutting

Plane-strain orthogonal cutting has recently been exploited as a means to refine the microstructure of metallic materials from tens of micrometers or greater to a few hundred nanometers. While experimental work has produced a significant body of knowledge with regard to microstructure and properties of machined materials, only a handful of studies can be found in the literature to discuss the microstructural evolution mechanism and to predict grain refinement during cutting. In this paper, dislocation density-based material models are developed to model grain size refinement and grain misorientation during cutting of Al 6061 T6 and OFHC Cu under various cutting conditions. It is shown that the developed CEL finite element model embedded with the dislocation material models captures the essential features of the deformation field and grain refinement mechanism during cutting. The model predicts the grains in the machined chips are refined from an initial size of 50–100 μm to about 100–200 nm for Al 6061 T6 and OFHC Cu at a low cutting speed of about 0.02 m/s with negative rake angle tools. It is shown that a small applied strain, high cutting speed or high cutting temperature will all contribute to a coarser elongated grain structure during cutting.     

脉冲电流密度对Ni-SiC镀层微观结构和显微硬度的影响

采用脉冲电沉积方法,在压缩机阀片表面制备Ni-SiC镀层。利用原子吸收分光光度计、透射电镜和硬度计研究脉冲电流密度对Ni-SiC镀层SiC粒子复合量、微观结构和显微硬度的影响。结果表明,随着脉冲电流密度的增大,Ni-SiC镀层SiC粒子的复合量先增加后略有降低。在脉冲电流密度为7A/dm2时,镀层SiC粒子的复合量高达9.92%(质量分数)。脉冲电流密度为7A/dm2时,镀层致密、晶粒细小,SiC粒子均匀分布于镀层中,且团聚现象较少。当脉冲电流密度为7A/dm2时,镀层的显微硬度高达842.9Hv。     

电解铜粉和雾化铜粉对SPS过程中显微组织演变的影响

以电解铜粉和雾化铜粉为SPS烧结原材料,对它们在SPS烧结过程中的烧结曲线、烧结体显微组织的演变过程,以及烧结温度对烧结体相对密度的影响进行了分析、比较,并分析了其中的原因。得到电解铜粉和雾化铜粉在SPS烧结过程中显微组织演变特征和规律不同的结论。     

Ordering effects on the microstructure and microhardness of nonstoichiometric titanium carbide TiCy

X-ray diffraction and microstructural studies show that, in the composition range TiC_0.50-TiC_0.70, annealing TiC _y at temperatures below 1073 K gives rise to the formation of Ti₂C and Ti₃C₂ ordered phases. The effect of ordering on the microstructure and microhardness of TiC _y is examined. In the course of annealing, grain growth reduces the microhardness of TiC _y , while ordering raises it.     

Evaluation of microstructure and properties deterioration in short fiber reinforced thermoplastics subjected to hydrothermal aging

The problem of quantitative characterization of damage accumulation during hydrothermal aging of polymer matrix composites is addressed. Effective elastic stiffnesses and thermal diffusivities of glass fiber reinforced thermoplastic are measured at several steps of aging. Anisotropic damage accumulation is identified. It is shown that both elastic and thermal properties of the composite degenerate with the accumulation of damage. The extents of degenerations are linked to each other using the methods of micromechanics. The established cross-property connection is in a good agreement with the experimental measurements.     

Role of aluminum ion implantation on microstructure, microhardness and corrosion properties of titanium alloy

Ti-Al-Zr alloy was implanted with Al at cumulative doses between 1 × 10¹⁷ and 1 × 10¹⁸ ions/cm². The results indicate that the Al-implanted layers are ∼0.1 μm thick and are composed almost entirely of an amorphous layer. Implanted layer hardness is dose dependent and is increased by more than a factor of 4 for the high-dose implanted specimen when compared with that of the substrate material. The corrosion resistance of the sample was markedly improved after aluminum implantation.     

Influence of the degree of order and nonstoichiometry on the microstructure and microhardness of titanium monoxide

The influence of the degree of order and nonstoichiometry on the microstructure of TiO _y titanium monoxide has been studied. The microstructure of substoichiometric, stoichiometric, and superstoichiometric titanium monoxide samples has been found to be determined by the presence of various ordered phases, which nucleate and grow in a matrix consisting of the high-temperature, cubic phase. The microhardness of titanium monoxide has been shown to depend on both nonstoichiometry and the degree of order, ranging from 9.9 to 14.0 GPa. The microhardness of the ordered monoxide exceeds that of the disordered monoxide, which is due to the formation of domains of an ordered phase, which hinder dislocation motion.     

钽基体上铜薄膜微观结构的分子动力学模拟

运用分子动力方法模拟了铜薄膜在钽（100）及（111）基体上沉积过程。结果表明沉积过程中铜薄膜的晶格位向取决于钽基体的晶格位向．在钽（100）面上，铜薄膜在不同的温度下分别沿（111）或（110）面生长，所形成的晶界与住错沿着薄膜的生长方向发展，薄膜表面的粗糙度与沉积温度有关，低温时表面粗糙度较大。而在钽（100）面上，铜薄膜的外延生长面为（100）面，位错沿（111）面分布，并只存在于界面附近，在铜薄膜的内部仅有少量的点缺陷，薄膜表面粗糙度较小并与沉积温度无关。     

拉伸变形纯铜的显微组织特征

为了研究多晶体中晶粒取向对其形变显微组织的影响,采用透射电镜定量表征了拉伸变形无氧高纯铜(0FHC)的显微组织,研究了形变显微组织与晶粒取向之间的相关性．结果表明：在晶粒内部形变显微组织均匀一致,而在不同晶粒之间则存在明显差异;根据位错组态的不同可将形变组织分为3种类型,即I型组织、Ⅱ型组织、Ⅲ型组织;不同类型形变显微组织与晶粒取向间存在明显的相关性．     

Development ofThiobacillus ferrooxidans ATCC 19859 strains tolerant to copper and zinc

A study was carried out to develop strains ofThiobacillus ferrooxidans ATCC 19859 tolerant to higher levels of heavy metal ions. Strains ofT. ferrooxidans capable of growing in Cu²⁺ (30 g/L) and Zn²⁺ (60 g/L) have been obtained. The ability of strains tolerant to either copper or zinc to grow in medium containing both the metals has been examined. The copper-tolerant strain (25 g/L) grows better in the medium containing both metals (Cu²⁺ 25 g/L and Zn²⁺ 40 g/L) compared to the zinc-tolerant strain (40 g/L).     

Analysis of microstructure and microhardness of Zr-2.5Nb processed by High-Pressure Torsion (HPT)

Nanostructured materials have been widely studied due to the improvement of their mechanical properties comparing to those of coarse grain materials. The present work intended to analyze the microstructure and microhardness of Zr-2.5Nb processed by high-pressure torsion (HPT), one of the severe plastic deformation techniques. The deformations were carried out at room temperature using a pressure of 5?GPa and 5 anvil turns. Vickers indentation was used to evaluate the microhardness of the samples. Transmission electron microscopy and X-ray diffraction were used to analyze the microstructure. The results showed a significant refinement from the initial microstructure achieving nanometric grain size around 50?nm and phase transformation α?→?ω?+?β_I induced by shear. The Vickers microhardness values of the material submitted to HPT technique were significantly higher than those of non-deformed material. Also, HPT procedure resulted in a huge grain refinement of the material and in phase transformation.     

Effect of vacuum heat treatment on microstructure and microhardness of cold-sprayed TiN particle-reinforced Al alloy-based composites

Cold spraying (CS) demonstrates great potentials in fabrication of metal matrix composites. The effect of post-spray heat treatment at 250 °C, 350 °C and 450 °C for 2 h on the microstructure and properties of CS Al5356/TiN composites was examined in this study. The results show that the heat treatment has little effect on the distribution of TiN particles in the matrix of all the composites. The pure Al5356 deposit presents large pores between the deposited particles after heat treatment, which is a common phenomenon for CS metallic coatings having an apparent increasing porosity during annealing. The adhesion between the deposit and substrate could be enhanced through atom diffusion, especially at elevated temperatures. However, the microhardness of all the deposits is significantly reduced after heat treatment because of the release of work-hardening effect within the as-sprayed metallic particles.     

Performance evaluation of sandwich panels subjected to bending compression and thermal bowing

The engineering performance of sandwich panels with expanded polystyrene foam core and steel or aluminium faces is evaluated in this paper. Such panels are usually used in semi-structural building applications with an insulating function. Bending, compression and thermal bowing experiments are conducted on these panels in the laboratory and their results are shown to conform in general to design values determined by current building codes and commercial practices. In edge-wise compression tests failure by column buckling has never occurred and localised face wrinkling is the usual failure mode. The adhesion between the polystyrene core and the metal skin as well as the location of the polystyrene joint in the panel are shown to have significant effects on the integral performance of the sandwich panels.     

Ultrasonic evaluation of spall damage accumulation in aluminum and steel subjected to repeated impact

This paper shows that the spall damage accumulated in target plates during repeated impact tests can be effectively evaluated by invoking ultrasonic techniques. The experimental data obtained for commercially available, pure aluminum and medium carbon steel subjected to three times repeated plate impact test, serve as a proof of efficiency and accuracy of our method. The spall damage was evaluated using a low frequency scanning acoustic microscope (C- and B-scan images) as well as measurement of ultrasonic velocity, attenuation (amplitude change of B2-B1 echo) and backscattering intensity. We provide here a detailed account of the damage history in essentially ductile aluminum. This proves that the voids nucleated during the first impact form the defect array undergoing coalescence when the stress of second impact is lower than the level applied in the first one. The case of aluminum contrasts the behavior of carbon steel, governed by the development of microcracks generated already during the initial impact. Our conclusions are based on the output of B- and C-scan images consistent with the results of ultrasonic measurements. While providing insights into the evolution of the spall damage, the non-destructive ultrasonic technique promoted by the present authors offers advantages of efficiency, direct applicability to the components of commercial structures, and for early damage prediction.     

Dynamic strains in architectural laminated glass subjected to low velocity impacts from small projectiles

An experimental validation of a mechanics-based finite element model for architectural laminated glass units subjected to low velocity, two gram projectile impacts is described. The impact situation models a scenario commonly observed during severe windstorms, in which small, hard projectiles, such as roof gravel, impact windows. Controlled experiments were conducted using a calibrated air gun to propel a steel ball against simply supported rectangular laminated glass specimens. Dynamic strains on the inner glass ply were measured using foil strain gages and a high speed data acquisition system. Impact speed, interlayer thickness, glass ply thickness, and glass heat treatment conditions were varied. Dynamic strains predicted by the finite element model were in close agreement with those measured in the laboratory.