Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.     

Effect of Copper Coating and Reinforcement Orientation on Mechanical Properties of LM6 Aluminium Alloy Composites Reinforced with Steel Mesh by Squeeze Casting

Uncoated and copper coated steel wire mesh reinforcing LM6 aluminium alloy composites have been produced using squeeze casting process by varying reinforcement orientation viz., 0°, 45° and 90° respectively. Microstructure of the castings has been examined and mechanical properties such as hardness, tensile strength and ductility have been investigated. Fracture surface of tensile specimens has been analysed using field emission scanning electron microscope. Microstructure of samples reveals that copper coating on steel wires improves the interface bonding between matrix and reinforcement. Average hardness values of 259 and 90 Hv have been observed in steel wire and matrix respectively. Tensile strength of composites increases with increasing angle of reinforcement orientation from 0° to 90°. Tensile strength increases up to 11% by reinforcing copper coated steel wire mesh at 90° orientation as compared to LM6 aluminium alloy. Fracture surface of composites shows pullout of steel wires in uncoated steel wire mesh composites and broken wires in copper coated steel wire mesh composites respectively. Dimples have been observed on the fracture surface of LM6 aluminium alloy. In general, copper coated steel wire mesh composites offer better hardness and tensile strength compared to uncoated steel wire mesh composites and LM6 aluminium alloy. This may be attributed to the copper coating on steel wires which results better interface bonding between matrix and reinforcement.     

Influence of Experimental Parameters on Friction and Wear Mechanisms of PA66/PTFE Blend Reinforced with Glass Fiber

Polymer blend of composition 80 wt% polyamide 66/20 wt% polytetraflurotheylene (PA66/PTFE) was selected as a matrix and reinforced with different weight percentage of short glass fibers (SGF). These composites were prepared by melt mix method using twin screw extruder followed by injection molding. The tribological behaviors were tested by using pin on disc machine by varying the different experimental parameters. The friction and wear mechanisms were studied as a function of sliding velocity, sliding load, and distance. The effect of fiber loading lowered the wear volume loss of SGF filled PA66/PTFE blend. The least frictional coefficient of 0.24 was obtained for 20 wt% of SGF in the blend. However, the wear resistance was not apparently improved by SGF loading in the experimental range for comparison with unfilled PA66/PTFE blend. The worn surfaces of specimen were examined by scanning electron microscopy photographs. The observations revealed that the frictional behavior was a function of development and formation of transfer film. Matrix wear and fiber wear were the result of frictional mechanism. The critical wear volume of PA66/PTFE/SGF composites was the contribution of both matrix and fiber wear. The abrasive nature of SGF was also one of the important factor for frictional behavior.     

Mechanical Properties and Dry Sliding Wear Behaviour of Molybdenum Disulphide Reinforced Zinc–Aluminium Alloy Composites

ZA-27 alloy is a lightest alloy which offers excellent bearing and mechanical properties in automobile and industrial applications. In this study, the MoS₂ particles with 0.5, 1 and 1.5 (wt%) weight percentages were reinforced in ZA-27 alloy to form composites, which were fabricated by using ultrasonic assisted stir casting method. The ZA-27/MoS₂ composite specimens were examined for chemical composition with the aid of XRD technique and EDS. Microstructure analysis of the ZA-27/MoS₂ composites was studied using SEM. Tests were conducted for mechanical properties such as tensile strength and hardness on ZA-27/MoS₂ composites samples as per ASTM standards. Dry sliding wear behavior of the composites was tested at various operating conditions by using pin-on-disc apparatus. Microstructural images of the ZA-27 composites reveal that there is a uniform dispersion of the MoS₂ particles in the base material. From the results it is observed that the mechanical properties increases with ZA-27 reinforced with 0.5 wt% MoS₂ composite and further decreases with increase in the filler content. The enhanced wear resistance is observed in ZA-27 reinforced MoS₂ composites as compared to the unreinforced alloy. The wear rate of the ZA-27 composites decreases with the increase in filler content, further the worn surfaces as examined using SEM reveals the wear mechanism explaining the improved wear resistance of the particulate composites.     

Fibridization Effect on the Mechanical Behavior of PA66/PTFE Blend Based Fibrous Composites

The use of natural fiber along with the glass fiber in polymer composites is one of the present material combinations for automotive industries. This article deals with the hybrid effect of 10 wt% short glass fibers (SGF) and 10 wt% short basalt fibers (SBF) on the mechanical behavior of 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend. These composite materials were prepared by melt mixing method, by using twin screw extruder followed by injection molding. The mechanical performance of the composite materials was tested as per ASTM method. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Hardness and density of the blended composites were also studied. Experimental results revealed that the effect of hybrid short fibers on the blend greatly enhanced the mechanical behavior. Increase in tensile strength and flexural strength by 33% and 57% respectively and 6% reduction in elongation was exhibited by the blend due to the hybrid effect of fibers. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The strain rate of the hybrid composites was deteriorated due to the hybrid effect. The enhancement of load carrying capacity by 17.35, 8.5 and 36% was exhibited by SGF, SBF and hybrid fiber filled PA66/PTFE blend composites respectively. The impact strength of the hybrid composites was reduced due to the brittle nature of the hybrid filled composites. Fiber fracture, fiber pull out and fiber misalignment were the certain mechanisms observed during mechanical performance. The fractured surfaces were analyzed through Scanning Electron Microscopy photographs.     

Correlation of tensile strength with fracture modes of KAOWOOL- and SAFFIL-reinforced 339 aluminum

The tensile strengths of composites of 339 aluminum reinforced with either SAFFIL or KAOWOOL fibers are compared over the temperature range of 20 °C to 300 °C. For this type of composite, in which the discontinuous fibers are randomly oriented, the fibers perpendicular to the applied stress play a critical role, which in turn creates a dependence upon the interfacial bond strength. The KAOWOOL fibers form a strong interfacial bond so that tensile failure occurs either in the matrix at 300 °C or by fiber cleavage at 20 °C. In the T5 condition, the SAFFIL interface is weaker than the matrix alloy so that failure occurs by delamination of the transverse fibers. Thus, although the SAFFIL fibers are 40 pct stronger than the KAOWOOL fibers, the T5 composites have the same ultimate tensile strengths. A T6 heat treatment promotes an interfacial reaction with magnesium. This strengthens the SAFFIL interface so that failure occurs primarily in the matrix, producing higher composite strengths. The reaction with the KAOWOOL fibers is so extensive that the matrix, and therefore the composite strength, is drastically decreased. When account is taken of the different fracture modes, together with the matrix strengths as determined by nanoindentation, the calculated values of composite strength are in good agreement with experiment.     

Correlation of tensile strength with fracture modes of KAOWOOL- and SAFFIL-reinforced 339 aluminum

The tensile strengths of composites of 339 aluminum reinforced with either SAFFIL or KAOWOOL fibers are compared over the temperature range of 20°C to 300°C. For this type of composite, in which the discontinuous fibers are randomly oriented, the fibers perpendicular to the applied stress play a critical role, which in turn creates a dependence upon the interfacial bond strength. The KAOWOOL fibers form a strong interfacial bond so that tensile failure occurs either in the matrix at 300 °C or by fiber cleavage at 20°C. In the T5 condition, the SAFFIL interface is weaker than the matrix alloy so that failure occurs by delamination of the transverse fibers. Thus, although the SAFFIL fibers are 40 pct stronger than the KAOWOOL fibers, the T5 composites have the same ultimate tensile strengths. A T6 heat treatment promotes an interfacial reaction with magnesium. This strengthens the SAFFIL interface so that failure occurs primarily in the matrix, producing higher composite strengths. The reaction with the KAOWOOL fibers is so extensive that the matrix, and therefore the composite strength, is drastically decreased. When account is taken of the different fracture modes, together with the matrix strengths as determined by nanoindentation, the calculated values of composite strength are in good agreement with experiment.     

Investigation of nickel metal powder on tribological and mechanical properties of Al-7075 alloy composites for gear materials

This research paper describes the fabrication of different weight percentages of (0–2?wt-%) nickel powder-filled aluminium alloy composites by stir casting techniques under a controlled environment. The physical, mechanical and tribological analyses of the nickel powder-filled aluminium alloy (Al-7075 series) composites are studied experimentally. The void content, Vickers hardness, compressive strength and impact strength of the unfilled and particulate-filled alloy composites are increased with the increase in filler content, while flexural strength of the composites shows reverse in trend. At the end, sliding wear analysis is performed to assess the wear performance of the unfilled and particulate-filled alloy composites. It is also observed that 2?wt-% nickel powder-filled alloy composite exhibits higher wear resistance as compared to other alloy composites. Finally, the microstructure analysis of the worn out composites is observed through scanning electron microscope to comprehend the wear mechanism of the composites for gear material application.     

Development of Wear Mechanism Map for Al–4Mg Alloy/MgAl 2 O 4 In Situ Composites

Dry sliding wear behaviour of Al–4Mg alloy and Al–4Mg alloy/MgAl2O4 in situ composites was examined under normal loads of 10–30 N at sliding speeds of 1, 3, 5 and 7 m/s and sliding distance of 1500 m using a pin-on-disc apparatus. Al–4Mg alloy with different wt% (1, 2 and 3) of MgAl2O4 in situ composites was synthesized via ultrasonic cavitation by the addition of H3BO3 powders. Unreinforced alloy and composites were characterized to conclude the role of MgAl2O4 in modifying the wear behaviour of the composite. Worn-out samples and wear debris were examined by scanning electron microscopy and X-ray diffraction in order to obtain the major wear mechanisms of the developed composites. The addition of MgAl2O4 significantly reduces the wear rate of Al–4Mg alloy at higher loads. The operating wear mechanisms observed were delamination, oxidation, abrasion, adhesive, thermal softening and plastic deformation modes.     

Dry Sliding Wear Behaviour of Ti–6Al–4V Alloy Consisting of Bimodal Microstructure

In the present paper, dry sliding wear behaviour of Ti–6Al–4V titanium alloy consisting of bimodal microstructure sliding against EN-31 steel at different sliding velocities (0.3, 0.6 and 0.9 m/s) and applied loads (60, 80 and 100 N) has been studied using a multiple Tribo tester and the results are presented. Two wear mechanisms have been identified irrespective of the applied load: oxidative wear occurs at the lowest sliding velocities and delamination wear occurs at the highest. Results indicated that by increasing the sliding velocity a transition from oxidative wear to delamination wear occurs with a corresponding minimum in the loss of volume due to wear. These results have been described by the analysis of the wear debris and that of the worn specimens using XRD, optical microscopy, FESEM and interpreted based on the metallurgical characteristics of titanium alloys which influence the wear resistance.     

Hybridization Effect on the Mechanical Behavior of Monophase Reinforced PA66/Teflon Blend Based Hybrid Thermoplastic Composites

The Monophase reinforced hybrid thermoplastic composites are the materials for the superior mechanical behavior. This article deals with the effect of single reinforcing phase (Fiber) in hybrid mode on the mechanical behavior of PA66/Teflon blend. Two hybrid material systems were selected: 10 wt% short glass fibers (SGF) and 10 wt% short carbon fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend (GB) and 10 wt% SGF and 10 wt% short basalt fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend(GB). These hybrid composite materials were prepared by melt mixing method by using twin screw extruder followed by injection molding. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Experimental results revealed that addition of hybrid short fibers into the blend greatly enhanced the mechanical behavior of PA66/PTFE composites. Increase in tensile strength by 46 and 33%, flexural strength by 45 and 57% for GC and GB composites respectively were observed. The GC composites had the better impact strength than GB composites. The peak load obtained was 36 and 48% higher than that of neat blend for GC and GB composites respectively were observed. The strain rate of the hybrid composites deteriorated due to the hybrid effect. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The hybrid effect increased the size of the voids and also the number of aggregates of the short fibers. This would weaken the reinforcement effect simultaneously building the strong bridge for the development of internal crack. Fractured surfaces were observed through Scanning Electron Microscopy photographs.     

Mechanical Properties and Tribological Behavior of Al6061–SiC–Gr Self-Lubricating Hybrid Nanocomposites

In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4–1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10–40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy.     

On the toughening of intermetallics with ductile fibers: Role of interfaces

The role of fiber debonding and sliding on the toughness of intermetallic composites reinforced with ductile fibers is examined. The toughness is shown to be a function of the matrix/fiber interface properties, residual stresses and the volume fraction, size and flow behavior of the fibers. Mechanical testing and in situ microstructural observations were carried out on a Ti-25at.%Ta-50at.%Al intermetallic matrix reinforced with W-3Re fibers. The fibers were coated with a thin oxide layer in order to induce debonding and prevent interdiffusion between the fiber and the matrix. The ductility, high strength and debond characteristics of coated tungsten-rhenium fibers promote a large increase in toughness. However, the mismatch in thermal expansion coefficients is the source of large residual tensile stresses in the matrix that induces spontaneous matrix cracking. Matrix cracking and composite toughness are examined as a function of the interfacial properties, residual stresses and properties of the fiber.     

Roles of Friction-Induced Strain Hardening and Recrystallization in Dry Sliding Wear of AZ31 Magnesium Alloy

Dry sliding wear tests were performed on AZ31 alloy using a pin-on-disc configuration under the loads of 5–360 N and sliding speeds of 0.1–1.5 m/s. Friction and wear characteristics of AZ31 alloy were investigated as a function of the load and sliding speed. Wear mechanisms for AZ31 alloy were characterized by scanning electron microscopy. The wear behavior in mild and severe wear regimes was described in terms of plastic deformation and microstructure evolution in subsurface, and surface hardness change and temperature rise of worn surfaces. The results revealed that surface strain hardening caused by large plastic deformation played an important role in maintaining a low slope of wear rate in mild wear regime, while surface thermal softening originating from dynamic recrystallization and surface melting were responsible for a rapid wear in severe wear regime.     

Enhancement of Tribological Properties of Al 6060 by Spray Coated TiO<Subscript>2</Subscript> Nanoparticle

Al 6060 alloy was coated with TiO₂ by spray pyrolysis technique at 400 °C using Titanium isopropoxide as precursor. The adhesion of the coating with the alloy was enhanced by annealing at 450 °C for 1 h which increased the hardness by 50%. Dry sliding wear resistance was experimented based on Taguchi’s L₂₇ array using pin-on-disc tribometer by varying parameters such as applied load (15, 25 and 35 N), sliding distance (500, 1000 and 1500 m) and sliding velocity (1.5, 2.5 and 3.5 m/s). Analysis of Variance predicted the major influence by load, followed by velocity and distance. Trend depicted an increase in wear rate with load and distance, whereas with velocity it decreased initially and then increased. Optimum condition for maximum wear resistance was determined from the Signal-to-Noise ratio. Experimental results were validated using regression equation with an error less than 3%. Scanning Electron Microscope analysis of the worn surfaces had revealed more defoilage and lay-off as the applied load was increased.     

AS41耐热镁合金的摩擦学行为研究

本文研究了AS41耐热镁合金在室温和200℃时的显微组织、力学和摩擦学性能,并探讨了其在高温的摩擦学机理。研究表明:AS41耐热镁合金主要由基体(α-Mg)相和第二相(Mg17Al12、Mg2Si和MgO相)组成,其在200℃时除延伸率有所增加外,抗拉强度和屈服强度均较室温时显著下降。耐热镁合金的摩擦系数随载荷增大而减小,滑行速度和滑行距离对摩擦系数的影响不大;磨损率随着载荷和滑行距离的增加而增大,但随滑行速度的增加而减小;且耐热镁合金在200℃的摩擦学性能优于其室温摩擦学性能。随着载荷变化,磨损机理发生变化;低载荷时表现为氧化磨损和磨粒磨损;中等载荷时表现为磨粒磨损和轻微剥层磨损;较高载荷时表现为剥层磨损。     

Study of Tribological and Mechanical Properties of A356–Nano SiC Composites

In the present investigation, the microstructural, wear, tensile and compressive properties of Al?C7Si alloy matrix nano composites have been discussed. It is noted that the composites contain higher porosity level in comparison to the matrix and increasing amount of porosity is observed with the increasing volume fraction of the reinforcement phase in the matrix. The wear sliding test disclosed that the wear resistance of the nano SiC reinforced composites is higher than that of the unreinforced alloy. It is believed that the presence of SiC particles could shield the matrix and silicon phase from directly experiencing the applied load from the counterface. It was revealed that the presence of nano-SiC reinforcement also enhanced the hardness, tensile and compressive yield strength of Al?C7Si alloy which can be attributed to small particle size and good distribution of the SiC particles and grain refinement of the matrix. The highest yield strength and UTS was obtained by the composite with 3.5?vol% SiC nano-particles. The results show that the addition of nano-particles reduces the elongation of A356 alloy.     

Effect of Prior Oxidation on Tensile Properties of Bare and Al3Ti Diffusion Aluminide Coated Near α Titanium Alloy Titan 29A

The effect of prior oxidation, for various durations up to 2,000 h in air at 650 °C, on the room temperature tensile properties of uncoated and Al₃Ti diffusion aluminide coated near α Ti alloy, Titan 29A, has been evaluated. The tensile properties of the uncoated alloy deteriorated with oxidation. Oxidation for just 100 h caused 11–13 % decrease in yield strength (YS) and ultimate tensile strength (UTS) of the alloy. The uncoated alloy exhibited brittle fracture within the elastic regime at significantly lower stress after oxidation for 2,000 h. On the other hand, the strength of the coated alloy remained unaffected even after 2,000 h of oxidation and the YS and UTS was similar to that of the un-oxidized alloy. The ductility of the coated alloy, however, decreased with the increase in oxidation duration. Such differences in the tensile behavior of the uncoated and coated alloy can be ascribed to the beneficial effect of the Al₃Ti diffusion aluminide coating in preventing surface embrittlement in the alloy during oxidation.     

Investigation on Mechanical and Adhesive Wear Behavior of Centrifugally Cast Functionally Graded Copper/SiC Metal Matrix Composite

The objective of this work is to fabricate functionally graded unreinforced copper alloy (Cu–10Sn) and a Cu–10Sn/SiC composite (Ø_out100 × Ø_in70 × 100 mm) by horizontal centrifugal casting process and to investigate its mechanical and tribological properties. The microstructure and hardness was analysed along the radial direction of the castings; tensile test was conducted at both inner and outer zones. Microstructural evaluation of composite indicated that the reinforcement particles formed a gradient structure across the radial direction and maximum reinforcement concentration was found at the inner periphery. Hence maximum hardness (205 HV) was observed at this surface. Tensile test results showed that, the tensile strength at inner zone of composite was observed to be higher (248 MPa) compared to that of the outer zone and unreinforced alloy. As mechanical properties showed better results at inner periphery, dry sliding wear experiments were carried out on the inner periphery of composite using pin-on-disc tribometer. Process parameters such as load (10–30 N), sliding distance (500–1500 m) and sliding velocity (1–3 m/s) were analyzed by Taguchi L₂₇ orthogonal array. The influence of parameters on wear rate was analyzed by signal-to-noise ratio and analysis of variance. Analysis results revealed that load (54%) had the highest effect on wear rate followed by sliding distance (18.2%) and sliding velocity (3.7%). The wear rate of composite increased with load and sliding distance, but decreased with sliding velocity. Regression equation was developed and was validated by confirmatory experiment. Worn surface of composite was observed using scanning electron microscopy and transition of wear was observed at all extreme conditions.