Materials Science Forum Vol. 1034

Abstract: One of the commonly used methods for the surface hardening treatment of pure titanium was nitriding. Based on the study of nitriding temperatures on the properties of the pure titanium, some conclusions can be drawn in this paper. The surface hardness of samples after nitriding was gradually increased firstly and then decreased with the processing temperature increasing. And the hardness of the diffusion layer reached the maximum value of 1792 HV when the processing temperature at 1050°C. At the same temperature, the indentation modulus also reached the maximum value of 270 GPa. The wear depth reached the minimum value at 1050°C. At different nitriding temperatures, the minimum of wear depth was 14.8 μm. In summary, when the processing temperature at 1050°C, the nitriding of pure titanium can improve the comprehensive properties.

Abstract: This study investigates the microstructure, tensile properties, and high-cycle fatigue resistance of twin-roll-cast Mg-3Al-1Zn (wt%) alloy strips with thicknesses of 1 mm, 1.5 mm, and 3 mm. The investigation results reveal that the 1-and 1.5-mm-thick strips show a fully dynamically recrystallized (DRXed) microstructure consisting of fine equiaxed DRXed grains, whereas the 3-mm-thick strip shows a partially DRXed microstructure containing very coarse elongated unDRXed grains because of the insufficient strain imposed during twin-roll casting. The inhomogeneous microstructure of the 3-mm-thick strip leads to a large deviation in its tensile elongation. The average grain size of the strips increases with increasing strip thickness, which results in reductions in both their tensile strength and their ductility because of the weakened grain-boundary hardening effect and the promoted formation of undesirable twins, respectively. The high-cycle fatigue resistance in the stress regime with finite fatigue life is similar for all three strips, but the fatigue strength with infinite fatigue life decreases from 175 MPa to 140 MPa as the strip thickness increases from 1 mm to 3 mm. The fatigue strength (FL) increases linearly with increasing yield strength (YS) according to the relationship FL = -199.5 + 2.03·YS.

Abstract: The recrystallization behavior of the cold-rolled AA3003 aluminum alloy with the reduction rate of 20%, 50% and 90% during annealing at the temperature ranging from 300°C to 400°C was investigated. As increasing reduction rate, the cold rolled specimens exhibit deformation bands with elongated grain microstructure consisting of straight grain boundary parallel to rolling direction. Therefore, large density of nucleation sites for recrystallization would be expected with increase of strain energy. The grain size of the cold-rolled specimens decreased with increase of reduction rate, c.f., as the rolling reduction increased to 90%, grain size along the direction normal to the sheet decreased to about 8μm in thick. When the sample annealed at 350°C for 5s, the first recrystallized grains were observed in the vicinity of the grain boundary. The relaxation and recrystallization kinetics under different annealing conditions were characterized in terms of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The apparent activation energies of recrystallization for the cold-rolled specimens with reduction rate of 20%, 50% and 90% were determined as 332 kJ/mol, 239 kJ/mol and 115 kJ/mol, respectively. XRD analysis by using modified Williamson–Hall plots revealed that the tendency of the change in dislocation density is varied depending on reduction rate. These results indicate that the apparent activation energy for recrystallization and the crystallites size decrease with increase of the reduction rate, which leads to a decrease in the size of the recrystallized grains.

Abstract: δ-ferrite was formed in the weld metal when the melted metal solidified to the room temperature. The δ-ferrite morphology depended on the composition, temperature gradient and growth rate. Research on the influence of heat treatment temperature (400°C, 600°C, 900°C) on the morphology changes and the δ-ferrite content is presented in this paper using optical microscopy, SEM, TEM. The δ-ferrite concentration reduced continuously in increasing temperature (from 23.5% after welding to 11% at 900°C for 10 hours). Besides, the formation of sigma phase and carbides at 600°C were the main cause of increasing hardness values in the fusion zone. However, the heat treatment at a temperature of 900°C eliminated both the sigma phase and brittleness.

Abstract: The present work investigates the mechanical characterization of aluminium alloy (AA) 6061 based hybrid nanometal matrix composites (MMCs) fabricated using conventional stir casting process. Two compositions viz., AA6061+1.5 wt.% B₄C+0.5 wt.% SiC (Hybrid A) and AA6061+1.5 wt.% B₄C+1.5 wt.% SiC (Hybrid B) was prepared and its mechanical properties such as microhardness, tensile, compressive, flexural and impact strength were investigated to compare with unreinforced AA6061. SiC and B₄C ceramic particles (purity 99.89%) of average particle size of 50 nm were used as reinforcements. Significant enhancement in microhardness of 30.2% and 31.02% for hybrid A and B are observed respectively. The ultimate tensile strength (UTS) increased by 10.72% and 16.55% for hybrid A and B respectively. Improved interaction because of the enhanced surface to volume ratio at the interface resulted in improvement of mechanical properties. Field emission scanning electron microscopy (FESEM) of the fractured surface shows brittle fracture because of the incorporation of the ceramic reinforcements in the matrix material. The developed AA6061/SiC/B­₄C hybrid nanocomposites show improved mechanical properties for high-performance structural applications.

Abstract: In the present investigation Aluminum matrix composites (AMMCs), Al7075 Alloy as matrix metal and Al₂O₃/SiC particles (2-8%) with an average particulate size of 20, 50 nm as strengthened material have been processed by the stir casting method. For the counter surface wear testing, a computerized pin on a wear tester was used as EN31 (58-60 HRC) steel disc and composite pin. The wear rate for the matrix metal and composites in terms of weight loss per unit sliding distance, friction coefficient, and volume loss were achieved. The composite results show better resistance to wear than matrix metal. SEM was used to investigate the microstructural characterization of worn surfaces. Sample weight loss was calculated and the change in cumulative wear loss at a sliding distance was uniform both for metal matrix as well as for composites. The wear speed for composites was also noted to be small compared to the metal matrix. In addition, experiments have shown that, with the increasing weight fraction of Al₂O₃/SiC and the coefficient of friction increases with increasing sliding velocity and weight fraction of Al₂O₃/SiC, the wear rate reduces. The wear characteristics (wear rate, coefficient of friction and wear loss) were better than those of other composites and the matrix metal with 6wt% Al₂O₃/SiC composites.

Abstract: In the present work, dry sliding wear characteristics of polytetrafluoroethylene (PTFE) composite reinforced with 35% by weight carbon fiber against AISI 304 stainless steel counterface is investigated with a view to consider PTFE composite as an alternative material for automotive applications. Dry sliding experiments were performed on pin-on-disk wear testing machine varying the normal load on pin, disk rotation (rpm) and temperature correlating with the range of pressure, sliding velocity and temperature variation at reciprocating conditions of compressor. A mathematical model to predict specific wear rate in terms of pressure and temperature was developed to understand parametric effect on wear rate. Specific wear rate has been observed to decrease with increase in pressure and temperature. Although, pressure (normal load) has been observed as more significant in lowering specific wear rate than temperature, no significant benefit was observed at higher ranges of pressure. Decrease in specific wear rate with increase in normal load (pressure) can be attributed to formation of transfer film at sliding interfaces. However, it is necessary to characterize transition of formation of transfer film varying with normal load and temperature respectively.

Abstract: The use of natural fibers in polymer matrix composites are increases because of their advantages like good stiffness, strength, environmental friendly, low cost and biodegradable. In the present investigation, hybrid fiber reinforced composites are fabricated using areca fiber and coconut shell powder (CSP) as reinforcement in epoxy resin. Unidirectional areca fiber and CSP reinforced epoxy composites were fabricated by varying the overall fiber loading (10, 20, 30, and 40 wt.%) and different weight ratios of areca fiber and CSP (1:1, 1:3, and 3:1). Effect of fiber loading and weight ratio on mechanical properties like tensile strength, tensile modulus, flexural strength, flexural modulus, interlaminar shear strength (ILSS), impact energy and surface hardness of hybrid composites were evaluate experimentally. All the hybrid composite samples fabrication and mechanical testing was done as per ASTM standards. The experimental investigation reveals that the tensile, flexural and ILSS properties show their maximum values at 30 wt.% of fiber loading with areca fiber and CSP weight ratio as 1:1. From the impact and hardness results it has been found that composites with areca fiber and CSP weight ratio as 3:1 and 1:1 respectively shows their maximum values at 40 wt.% of fiber loading. Interfacial analysis of the hybrid composites were also observed by using scanning electron microscope (SEM).

Abstract: Porosity is one of the main difficulty to fabricate the superior quality of aluminium matrix composites (AMCs) because it effects the surface finish of the casting, mechanical properties and corrosion resistance. Therefore, porosity must be minimum as possible so that better casting can be produced with optimal properties of the composites. In this study, aluminium matrix nanocomposites (A356/SiC or AMNCs) were fabricated through two-step stir casting via mechanical alloying using ball mill. The matrix alloy (A356) was reinforced with SiC nanoparticles of 40-55 nm avarage particle size (APS). The corrosion was performed by simple immersion corrosion test method for a predefined environment (3.5% NaCl solution) and for the specified duration. The results showed that density and porosity increase with the addition of reinforcement. The corrosion resistance get reduced with the incorporation of SiC due to the increase in porosity and number of nucleation sites. The substantial correlation between the corrosion rate and the amount of SiC are depicted. Moreover, the corrosion rate decreased with the increase in exposure time which is due to the formation of passive layer. The EDS spectrum shows the presence of different constituents in the composites. The formation of the cracks, oxides, pitting corrosion, and localized corrosion are found by the SEM results. Further, SEM of the corroded surface verifies the presence and good distribution of the SiC nanoparticles in the fabricated nanocomposites.