Nanoindentation studies and analysis of the mechanical properties of Ti-Nb2O5 based composites

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Fracture Toughness (K1C) evaluation for dual phase medium carbon low alloy steels using circumferential notched tensile (CNT) specimens

The fracture behavior of dual phase medium carbon low alloy steels produced using two different chemical compositions (A - 0.34C, 0.75Mn, 0.12Cr, 0.13Ni steel and B - 0.3C, 0.97Mn, 0.15Cr steel) was investigated using circumferential notched tensile (CNT) specimens. Intercritical treatments were performed on samples with composition A by 1) austenitizing at 860 °C for 1 hour cooling in air, then treating at 770 °C for 30 minutes before oil quenching; 2) austenitizing at 860 °C for 1 hour quenching in oil, then treating at 770 °C for 30 minutes before quenching in oil; and 3) austenitizing at 860 °C for 1 hour, super-cooling to 770 °C and then quenching in oil. Samples of composition B were subjected to intercritical treatment at temperatures of 740, 760, and 780 °C for 30 minutes, followed by quenching rapidly in oil. Tensile testing was then performed on specimens without notches and the CNT specimens. It was observed that the dual phase steel produced from procedure (2) yielded a fine distribution of ferrite and martensite which gave the best combination of tensile properties and fracture toughness for composition A while the dual phase structure produced by treating at 760 °C yielded the best combination of tensile properties and fracture toughness for composition B. The fracture toughness results evaluated from the test were found to be valid (in plain strain condition) and a high correlation between the fracture toughness and notch tensile strength was observed. The fracture toughness values were also found to be in close agreement with data available in literature

Mechanical behaviour and damping properties of Ni modified Cu–Zn–Al shape memory alloys

The microstructure, mechanical behaviour and damping properties of Cu–18Zn–7Al–xNi alloys (where x = 0.1, 0.2, 0.3 and 0.4) were investigated. The Cu–Zn–Al alloys were produced by casting and then subjected to a homogenization – cold rolling – annealing treatment scheme. Optical-, scanning electron-microscopy and X-ray diffraction analysis were utilized for structural characterization of the alloys, while tensile test, fracture toughness, and hardness measurement were used to assess the mechanical properties. The results show that all the alloy compositions consisted of the predominating CuZn phase. Sharp edged elongated grain structures were observed in the unmodified and the 0.4% Ni modified CuZnAl alloys, while the 0.1, 0.2 and 0.3 %Ni modified CuZnAl alloy compositions, had more of granular/curved/round grain edges and smaller grain widths. The hardness of the unmodified CuZnAl alloy (294.5 ± 2.08 VHN) was lower than that of the Ni modified CuZnAl ones with an increase in hardness ranging between 23.5 and 38.4%. The tensile strength, the percentage elongation (10.7–14.3%) and the fracture toughness of the 0.1, 0.2 and 0.3% Ni modified CuZnAl alloys were observed to be higher than those of the unmodified and the 0.4 %Ni modified CuZnAl alloys. The 0.2% Ni modified CuZnAl alloy had the highest damping capacity among all compositions under investigation, while the 0.4% Ni modified one showed the least capacity to serve as a damping material. Keywords: CuZnAl alloys, Shape memory capacity, Micro-alloying, Mechanical behaviour, Damping properties, Structural characterizatio

Recrystallization mechanisms and microstructure development in emerging metallic materials: A review

This review is devoted to the understanding of the recrystallization mechanisms and its role in the control of the microstructure in emerging metallic materials. Recrystallization is a very pervasive transformation phenomenon that is considered to be very important in efficient microstructure designs. Currently, there is hardly any work which has attempted to present a concise and systematic review of the recrystallization in emerging materials with a view to reconcile its manifestations with trends established from recrystallization studies in traditional alloys. This review aims to address this by first reviewing the fundamental and nascent recrystallization mechanism concepts and then analyzing their forms in emerging metallic materials, such as high strength steels, Ti- and Mg-based alloys, as well as high-entropy and shape-memory alloys. The reviews on these systems show that the classic recrystallization concepts are still relevant for explaining the recrystallization behavior and by extension to the microstructure development in the materials. However, in some instances, structural factors exclusive to these materials influenced the driving force and recrystallization behavior yielding outcomes sufficiently distinct from that observed in traditional alloys. Basically, deformation processing and material factors such as stress accumulation, inhomogeneous strain distribution, stored energy, available slip systems, phase composition, microstructural variability, initial grain size, texture, stacking fault and lattice distortion energies, strain path, deformation temperature, and solute clustering and diffusion rates were at play in determining the recrystallization mechanisms and kinetics in these emerging metallic materials. Keywords: Recrystallization mechanisms, Microstructure, Deformation processing, Stored energy, Emerging metallic material

Evaluation of the damping behaviour of Al-Mg-Si alloy based composites reinforced with steel, steel and graphite, and silicon carbide particulates

Metallic materials known for their good toughness and ductility are now contemplated as replacements to the inherently brittle ceramics which are typically used as reinforcements in aluminium based composites (AMCs), because of the growing structural applications of AMCs. However, the good damping properties offered by the ceramic reinforced AMCs have not been well studied in their metallic reinforced counterparts. The present study investigates and compares the damping behaviour of Al-Mg-Si alloy based composites reinforced with 6 and 8 wt% steel particles to that reinforced with a hybrid mix of 6 wt% steel and 2 wt% graphite, and 8 wt% SiC particles. The aluminium based composites were produced using stir casting process and the microstructures characterised with backscattered electron mode imaging. A dynamic mechanical analyser was used to evaluate the damping properties of the composites produced. The results show that the storage modulus of the composites containing 8 and 6 wt% steel particles were higher than that of the other composite grades with the 8 wt% SiC reinforced composite composition recording the lowest value. The Aluminium based composite containing 8 wt% steel particles also had the highest loss modulus over the test temperature range (70–250 °C) but because of its relatively higher storage modulus, it did not record the best damping capacity which was obtained with the 8 wt% SiC reinforced composite. The effect of the test frequencies 5 Hz and 10 Hz on the damping properties was on the average marginal, while significant variation in damping properties with test temperature were observed in the study. Keywords: Aluminium based composites, Metallic reinforcement, Steel particles, Dynamic mechanical analyser, Damping capacity, Storage modulu

Mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips

The mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips was investigated in this research. Steel machining chips with chip size range of 105 μm and below were utilized to develop stir cast copper matrix composites having 5, 7.5 and 10 wt% of the chips as reinforcement. Unreinforced copper and 10 wt% alumina reinforced copper matrix composites were also prepared for control experimentation. Hardness and tensile properties evaluation, wear test, potentiodynamic polarization corrosion tests, and optical microscopy; were used as basis to characterize the composites produced. The results show that the addition of steel machining chips in copper resulted in significantly low porosity levels in the copper matrix composites compared with the use of alumina as reinforcement. The mechanical properties (hardness and tensile properties) and wear resistance were also observed to improve with the use of the steel machining chips as reinforcement. The corrosion susceptibility in 3.5 wt% NaCl solution were observed to be more intense for the unreinforced copper and the alumina reinforced composite grade compared with the steel chips reinforced copper matrix composites. But in 0.3 M H2SO4 solution, no consistent corrosion trend was observed although the corrosion resistances of all the composite grades produced were superior to the unreinforced copper. The results demonstrate the capacity of steel machining chips to serve as a reliable cost effective and technically efficient reinforcement material for the development of copper matrix composites

Reconciling viability and cost-effective shape memory alloy options – A review of copper and iron based shape memory metallic systems

Shape memory alloys (SMAs) are group of alloys that display anthropomorphic characteristics. These alloys recover their pre-deformed morphology when heated above their transition temperatures after being deformed in their lower temperature phase (martensitic phase). This unique material behavior is explored in industrial and technological applications where capacity for strain recovery is a key design parameter. Copper and iron based SMAs are largely viewed as potential cost effective substitute to Ni–Ti SMAs judging from their promising shape memory properties, damping capacity and other functional properties. Despite their outstanding potentials, the susceptibility of copper based SMAS to phase stabilization, transition hysteresis, aging and brittleness creates doubt on the possibility of transiting from the realm of potential to functional long term use in engineering applications. On the other hand the low percentage shape recovery in the Fe based SMAs also creates a gap between the theory and potential use of these alloys. This paper takes a critical look at the science of shape memory phenomena as applicable to copper and iron based SMA systems. It also covers the limitations of these systems, the effect of processing parameters on these alloys, proposed solutions to limitations associated with this group of shape memory alloys and thoughts for future consideration