Volume Fraction Of Hard Phase Research Articles

Effect of Carbon Content and Hard Phase Volume Fraction on Yield Strength in Friction Stir Processing of Low and Medium Carbon Steels

Effect of Carbon Content and Hard Phase Volume Fraction on Yield Strength in Friction Stir Processing of Low and Medium Carbon Steels

Friction stir processing: An effective thermo-mechanical processing technique for carbon steels

This review paper deals with the detailed study of published research work on FSW/FSP of different types of steels and post processing such as heat treatment effects on additively manufactured steel beads. In this context, it comprises of post processing effects on steel beads fabricated by additive manufacturing technique that includes different techniques like selective laser melting (SLM), Laser-TIG (Tungsten inert gas), Metal inert gas welding, etc. along with post processing techniques such as hot iso-static pressing (HIP), conventional heat treatment (HT), post weld heat treatment (PWHT), etc. Also, it consists of the pros and cons of FSW/ FSP, especially on low and medium carbon steels. Moreover, this paper is mainly related to the effects of friction stir welding/ processing on the evolution of microstructure, weld morphology, and temperature gradients in the processed region. In addition, there are detailed analyses of tool selection, effect of weld pitch ratio, effect of carbon content (Wt. %), and hard phase volume fraction on yield strength i.e. carbide distribution in the FSP low and medium carbon steels, and their correlation with the mechanical responses as well as crystallographic orientation relationship. Finally, based on published research, gaps are highlighted and presented as future scope of research work.

A Study on the Interrelationship between the Microstructural Features and the Elevated Temperature Strength of Multicomponent Al-Si-Cu-Ni Casting Alloys

The elevated temperature strength of multicomponent Al-Si alloys is greatly affected by the volume fraction and the interconnectivity of hard phases formed upon solidification. In the present investigation, such influences were examined for two Al-Si-Cu-Ni alloys with different total volume fractions of hard phases. To control the microstructural features related to the size of the phase, the specimens were prepared with and without ultrasonic melt treatment (UST) at different cooling rates. The microstructures of the alloys were composed of primary Si, eutectic Si, (Al,Si)3(Zr,Ni,Fe), Al9FeNi and Al3(Cu,Ni)2 phases. The microstructural features, such as the size and aspect ratio of each phase, changed with UST and cooling rate, and accordingly, the elevated temperature strength at 350 oC was changed. The alloy with a high volume fraction of about 30 vol.% exhibited increased elevated temperature strength at 350 oC when ultrasonic melt treated, and the alloy having a volume fraction as low as about 18 vol.% exhibited the opposite results. Considering the microstructural features of the multi-component Al-Si alloy, a hexagonal shear-lag model was suggested, based on the well-known shearlag model proposed by Nardone and Prewo (Scr. Metall. 20;1986:43-48). Using the 2-D microstructural factors such as the size, aspect ratio of the phase and secondary dendrite arm spacing, the elevated temperature strength was calculated and compared with the measured value. Based on the hexagonal shear-lag model, the influence of microstructural factors on the elevated temperature strength was discussed for multi-component Al-Si-Cu-Ni alloys.

Comparison of Structure and Properties of Mo2FeB2-Based Cermets Prepared by Welding Metallurgy and Vacuum Sintering.

At present, most Mo2FeB2-based cermets are prepared by vacuum sintering. However, vacuum sintering is only suitable for ordinary cylinder and cuboid workpieces, and it is difficult to apply to large curved surface and large size workpieces. Therefore, in order to improve the flexibility of preparing Mo2FeB2 cermet, a flux cored wire with 70% filling rate, 304 stainless steel, 60 wt% Mo powder and 40 wt% FeB powder was prepared. Mo2FeB2 cermet was prepared by an arc cladding welding metallurgy method with flux cored wire. In this paper, the microstructure, phase evolution, hardness, wear resistance and corrosion resistance of Mo2FeB2 cermets prepared by the vacuum sintering (VM-Mo2FeB2) and arc cladding welding metallurgy method (WM-Mo2FeB2) were systematically studied. The results show that VM-Mo2FeB2 is composed of Mo2FeB2 and γ-CrFeNi.WM-Mo2FeB2 is composed of Mo2FeB2, NiCrFe, MoCrFe and Cr2B3. The volume fraction of hard phase in WM-Mo2FeB2 is lower than that of VM-Mo2FeB2, and its hardness and corrosion resistance are also slightly lower than that of VM-Mo2FeB2, but there are obvious pores in the microstructure of VM-Mo2FeB2, which affects its properties. The results show that WM-Mo2FeB2 has good diffusion and metallurgical bonding with the matrix and has no obvious pores. The microstructure is compact and the wear resistance is better than that of VM-Mo2FeB2.

Development of a gall-resistant stainless-steel hardfacing alloy

This work details the development of a new cobalt-free stainless steel powder metallurgy hardfacing alloy designed to replace Stellite 6, a cobalt-based hardfacing alloy used in nuclear valve applications. The fundamental strategy centers on alloying stainless steels with up to 0.5 wt% nitrogen, which is shown to increase both the volume fraction of hard phase precipitates and the strain-hardening rate of the matrix. The resultant alloy, Nitromaxx, exhibits galling performance that is comparable to Stellite 6, up to 350 °C. This performance is attributed to the suppression of strain localization events associated with galling. In particular, transmission electron microscopy and diffraction measurements from tensile tests show that the nitrogen addition decreases the calculated matrix stacking fault energy and enhances both deformation-induced martensite transformation at room temperature and deformation twinning at elevated temperature. These strain-hardening mechanisms, coupled with the increase in precipitate volume fraction, effectively suppress localization and enhance galling resistance up to 350 °C. The enhanced galling resistance cannot be rationalized in terms of tensile stress-strain response alone.

Mechanical properties of nanostructured films with an ultralow volume fraction of hard phase

We demonstrate in this paper how polymerization induced self-assembly (PISA) using RAFT can be used to synthesize very asymmetric but monodisperse poly(acrylic acid)-b-poly(n-butyl acrylate) block copolymers, PAA-b-PBA, with a short PAA block and a long PBA block. In the course of the surfactant-free emulsion polymerization, core-shell particles form in water, with the short hydrophilic block located at the water-particle interface, and the long hydrophobic block constituting the particle core. Drying at room temperature creates films possessing an out of equilibrium structure, where the glassy PAA block generates a percolating network of shells. When deformed in uniaxial elongation, these films combine a high stiffness in small strains (considering the low volume fraction of PAA, of only 3 wt%), a yield stress and a significant extensibility before failure. The modulus, yield stress and extensibility can be tuned by modifying the composition of the latex serum with cations or positively charged low molar mass polymers, or by changing the copolymer composition. Of particular interest was the synthesis by PISA of particles of triblock copolymer PAA-b-PBA-b-PS. The out of equilibrium structure obtained had a very interesting combination of high stiffness, extensibility and high fracture toughness.

Needle Like Fe-Containing Intermetallic Compounds of High Silicon Aluminum Alloy with Fe Modified by Mn and Ultrasonic Vibration

In this study, the modification effects and mechanism of manganese (Mn) and ultrasonic vibration (USV) on the needle-like Fe-containing intermetallic compounds of Al-20Si-xFe-2.0Cu-0.4Mg-1.0Ni (x=1, 2 wt.%) alloy have been studied respectively. The effect of Fe-containing phases on volume fraction of hard phases is also investigated. The results show that the mechanism and effect of Fe-containing intermetallic compounds improved by Mn are in close relationship with Fe content. Mn can promote to form less harmful α-Al15(Fe,Mn)3Si2 phase, or replace some Fe atoms of β-Al5FeSi and δ-Al4FeSi2 according to different Fe content. When USV was applied to this alloy containing 2%Fe near liquidus temperature, most of the acicular β phases formed in traditional process are substituted by fine plate δ phases. With the combined effects of 0.5%Mn and USV, the acicular β phases are almost repressed and the Fe-containing phases exist in form of fine Al4(Fe,Mn)Si2 and Al5(Fe,Mn)Si particles about 20~30μm. Consequently, the total volume fraction of hard phases which are composed of primary silicon particles and Fe-containing phases increases significantly.

Competing damage mechanisms in a two-phase microstructure: How microstructure and loading conditions determine the onset of fracture

This paper studies the competition of fracture initiation in the ductile soft phase and in the comparatively brittle hard phase in the microstructure of a two-phase material. A simple microstructural model is used to predict macroscopic fracture initiation. The simplicity of the model ensures highly efficient computations, enabling a comprehensive study: a large range of hard phase volume fractions and yield stress ratios, for wide range of applied stress states. Each combination of these parameters is analyzed using a large set of (random) microstructures. It is observed that only one of the phases dominates macroscopic fracture initiation: at low stress triaxiality the soft phase is dominant, but above a critical triaxiality the hard phase takes over resulting in a strong decrease in ductility. This transition is strongly dependent on microstructural parameters. If the hard phase volume fraction is small, the fracture initiation is dominated by the soft phase even at high phase contrast. At higher hard phase volume fraction, the hard phase dominates already at low phase contrast. This simple model thereby reconciles experimental observations from the literature for a specific combination of parameters, which may have triggered contradictory statements in the past. A microscopic analysis reveals that the average phase distribution around fracture initiation sites is nearly the same for the two failure mechanisms. Along the tensile direction, regions of the hard phase are found directly next to the fracture initiation site. This ‘band’ of hard phase is intersected through the fracture initiation site by ‘bands’ of the soft phase aligned with shear. Clearly, the local mechanical incompatibility is dominant for the initiation of fracture, regardless whether fracture initiates in the soft or in the hard phase.

Effects of V Addition on Microstructure and Hardness of Fe-C-B-Ni-V Hardfacing Alloys Cast on Steel Substrates

Fe-based hardfacing alloys containing high volume fraction of hard phases are a suitable material to be deposited as wear resistant thick coatings. In the case of alloys containing high amount of interstitial alloying elements, a key factor affecting the performance is dilution with the substrate induced by the coating process. The present research was focused on the analysis of V-bearing Fe-based alloys after calibrated carbon and vanadium additions (in the range from 3 to 5 wt.%) to a commercial Fe-C-B-Ni hardfacing alloy. Vanadium carbides with a petal-like morphology were observed in the high-V hypereutectic alloys allowing to reach hardness values above 700 HV. The solidification range shifted to higher temperatures with increasing amount of vanadium addition and in the case of hypereutectic alloys, the gap remains close to that of the original alloy. In the last step of the research, the microstructural evolution after dilution was analyzed by casting the V-rich alloys on a steel substrate. The dilution, caused by the alloying element diffusion and the local melting of the substrate, modified the microstructure and the hardness for a relevant volume fraction of the hardfacing alloys. In particular, the drop of interstitial elements induced the transition from the hypereutectic to the hypoeutectic microstructure and the formation of near-spherical V-rich carbides. Even after dilution, the hardness of the new alloys remained higher than that measured in the original Fe-C-B-Ni alloy.

Finite Element Simulation of the Distribution of Micro-Stress and Strain of Multiphase Steel

By using the finite element method (FEM), the stress-strain curves of multiphase steels was simulated based on the stress-strain curves of single-phase ferrite, bainite, and martensite steels; then the measured result was compared with the simulated one. Effective factors such as the different distribution of microstructure, the volume fraction of hard phase and the yield stress ratio between single-phase hard phase steel with single-phase ferrite steel in multiphase steel are discussed in this work. The results show that the simulated result closely fits the measured one, which proves that this FEM built in this work is correct. The coarser the microstructure, the higher the drag effects of bulk structure, and the larger deformation degree of ferrite phase. With the increase of bainite and martensite volume fraction, the maximum stress rise gradually and the maximum strain decreases gradually. Meanwhile, the effects of volume fraction of hard phase on the stress-strain curve of multiphase steels are larger than that of yield stress ratio between single-phase hard phase steels and single phase ferrite steel.

Influences of phase composition and thermomechanical conditions on shape memory properties of segmented polyurethanes with amorphous reversible phase

AbstractWe synthesized series of shape memory polyurethanes with amorphous reversible phase (Tg‐SMPUs) and systematically studied their microphase structure and shape memory properties. The Tg‐SMPUs having no or less hard phase showed lower shape recovery. When the volume fraction of hard phase was in the range of 20–30%, the Tg‐SMPUs exhibited the highest shape recovery. As the fraction of hard phase increased further the shape recovery decreased, because more polymer components with higher glass transition temperatures (Tgs) would participate in strain storage. For the Tg‐SMPUs having similar Tgs, those polymers having higher volume fraction of hard phase exhibited higher shape fixity, broader shape recovery region, and larger recovery stress. Increasing deformation strain could raise shape fixity and recovery stress but broaden shape recovery region. The highest recovery stress of a material could be achieved when the deformation occurred at its glass transition temperature below which decreasing deformation temperature could not increase recovery stress further. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Comparison of Work Hardening Behaviour of Ferritic-Bainitic and Ferritic-Martensitic Dual Phase Steels

In this research, the stress-strain curves of two types of dual phase steels, namely ferritic-bainitic and ferritic-martensitic steels with 0.16%C and 1.2% Mn have been obtained using tensile tests. Both steels were intercritically annealed under different conditions and the ferritic bainitic steels subsequently quenched in a salt bath, while the ferritic martensitic steels were water quenched. The stress-strain data of the specimens were checked using Hollomon's equation. The results showed that both types of dual phase steels had two stages of work hardening and each stage had a different work hardening exponent. The effects of volume fraction of hard phases (bainite and martensite) on ultimate tensile strength, total elongation and work hardening exponent were also investigated. The results indicated that with increasing volume fraction of hard phase the UTS was increased whereas the work hardening exponent and total elongation were decreased.

Fracture-Toughness Analysis in Transition-Temperature Region of Three American Petroleum Institute X70 and X80 Pipeline Steels

The fracture toughness in the transition-temperature region of three American Petroleum Institute (API) X70 and X80 pipeline steels was analyzed in accordance with the American Society for Testing and Materials (ASTM) E1921-05 standard test method. The elastic-plastic cleavage fracture toughness (K Jc ) was determined by three-point bend tests, using precracked Charpy V-notch (PCVN) specimens; the measured K Jc values were then interpreted by the three-parameter Weibull distribution. The fracture-toughness test results indicated that the master curve and the 98 pct confidence curves explained the variation in the measured fracture toughness well. The reference temperatures obtained from the fracture-toughness test and index temperatures obtained from the Charpy impact test were lowest in the X70 steel rolled in the two-phase region, because this steel had smaller effective grains and the lowest volume fraction of hard phases. In this steel, few hard phases led to a higher resistance to cleavage crack initiation, and the smaller effective grain size led to a higher possibility of crack arrest, thereby resulting in the best overall fracture properties. Measured reference temperatures were then comparatively analyzed with the index temperatures obtained from the Charpy impact test, and the effects of microstructures on these temperatures were discussed.

Characterizations of cold-sprayed Nickel–Alumina composite coating with relatively large Nickel-coated Alumina powder

Previous studies have shown that the fabrication of metal matrix composites (MMCs) by cold spraying is effective and promising. When light materials, such as SiC and Al 2O 3, were used as reinforcements, it was diffcuclt to obtain a high volume fraction of hard phase in the composite just through the simple powder mixture. Therefore, in this study, a Ni-coated Al 2O 3 powder, which was produced through hydrothermal hydrogen reduction method, was employed aiming at increasing the volume fraction of ceramic particles in the deposited composite coating. It was found that a dense Ni–Al 2O 3 composite coating could be deposited with the Ni-coated Al 2O 3 powder under the present spray conditions. X-ray diffraction analysis indicated that the composite coating had the same phase structures as the feedstock. The volume fraction of Al 2O 3 in the composite was about 29 ± 6 vol.%, which is less than that in the feedstock (nominal: 40–45 vol.%) due to the rebound of some Al 2O 3 particulates upon kinetic impacting. The microhardness of the composite coating was about 173 ± 33Hv 0.2.

Phase distribution, grain size and coercivity in nanocomposite permanent materials

Phase distribution and grain size are the key factors controlling the coercivity in nanocomposite permanent magnets. Assuming three simple physical models with different phase distributions, we have calculated the dependence of coercivity on the grain size and volume fraction of hard phase by using the statistical mean. The calculations show that the different phase distributions leads to the variation of the dependence of coercivity on the grain size and volume fraction of hard phase. High coercivity can be probably obtained by designing an ideal phase distribution with the clusters of soft grains and controlling the hard grain size. Besides, the calculated results also indicate that the experimental enhancement of the coercivity with reducing hard grain size depends on the effects of the grain size and phase distribution on the fraction of soft–hard grain interface.

Dependence of coercivity on phase distribution and grain size in nanocomposite Nd 2 Fe 14 B/α–Fe magnets

The dependence of coercivity on the grain size in nanocomposite Nd2Fe14B/α–Fe magnets with different distributions of magnetically soft and hard phases is investigated by means of statistical mean. The calculations show that when there exists no soft phase, the coercivity of magnets decreases monotonically with hard grain size reducing. For a given volume fraction of hard phase, the coercivity of nanocomposite Nd2Fe14B/α–Fe magnets with a random distribution of soft and hard grains shows a peak value as a function of hard grain size. When the hard grain size is larger than an optimum value of soft grain size (15nm), the nanocomposite Nd2Fe14B/α–Fe magnets with the multilayer structure of soft and hard grains can possess a higher coercivity than that with the random distribution of soft and hard grains.

Optimization of stress-strain behavior parameters by genetic algorithms method: Application to soft-matrix two-phase alloys

Deformation behavior of soft-matrix two-phase alloys has been computed using a continuum mechanics model based on an Isostrain condition, while the stress is distributed by the rule of mixtures. A genetic algorithm (GA) was used to optimize the mechanical modeling parameters such as the resistance and the formability of each phase. The stress–strain curves have been calculated as a function of volume fraction and mechanical properties of phases. The calculated and experimental stress–strain curves are compared and good agreement is found. The resistances increases with the rise of the hard phase volume fraction; this is more important with the presence of the hard phase than with the soft one. A linear law of variation of the phase resistance allows to interpolate and extrapolate the model, a good agreement is found with the evolution of the mechanical behavior.

The significanc of crack tip deforming for short and long fatigue cracks : Hammouda, M.M.I., El-Sehily, B.M. and del los Rios, E.R. Fatigue and Fract. Eng. Mater. Struct. (1996) 19 (4), 475–484

The rolling-sliding dry-wear behaviour of a series of bainitic steels and a pearlitic rail steel has been investigated over a wide range of contact stress and creepage conditions. A wear-testing machine designed and built at Leicester — LEROS — allows very high contact stresses to be combined with high creepages under well-controlled conditions. Despite better standard mechanical properties, the wear resistance of the lower carbon bainitic steels was inferior to that of the pearlitic steel. A bainitic steel of the same carbon content as the pearlitic steel wore a little less, but at considerable expense to the counter-material in the wear couple. The wear resistance of the bainitic steels depends on the volume fractions of hard phases, carbide and martensite-austenite phase, for rolling-sliding as well as other types of dry-wear loading. Pearlite performs exceptionally well under rolling-sliding conditions since the lamellar microstructure is modified so as to present a greater area fraction of hard carbide plates at the wear surface, a fraction in excess of the bulk volume fraction of carbide. Recommendations are made for the application of these steels in rolling-sliding and other dry-wear circumstances.

Scoring of Precision Spur Gears

Abstract A group of manufacturing machines employed precision spur gears as the timing mechanism for machine operations. These machines had worked successfully for about ten years with little or no problems with gear wear or deterioration. When new machines were brought on line with recently made gears there were immediate problems with gear tooth scoring. A laboratory study was conducted to determine if metallurgical conditions were related to the gear scoring. Recent gears were made from a modification of the alloy used in early gears. The new alloy had been modified to make it more resistant to softening in coating operations. Reciprocating wear tests and galling tests were conducted to compare the tribological characteristics of the old and new gear steels. It was determined that the threshold galling stress of the gear steels was strongly dependent on the hardness. The reciprocating wear tests indicated that the wear resistance was affected by the volume fraction of hard phases in the steels. The recommended short-term solution was to alter the tempering procedure for the steel to keep Rockwell C hardness above 60; the long-term solution was to change the gear material and lubrication.

Dry rolling-sliding wear of bainitic and pearlitic steels

The rolling-sliding dry-wear behaviour of a series of bainitic steels and a pearlitic rail steel has been investigated over a wide range of contact stress and creepage conditions. A wear-testing machine designed and built at Leicester — LEROS — allows very high contact stresses to be combined with high creepages under well-controlled conditions. Despite better standard mechanical properties, the wear resistance of the lower carbon bainitic steels was inferior to that of the pearlitic steel. A bainitic steel of the same carbon content as the pearlitic steel wore a little less, but at considerable expense to the counter-material in the wear couple. The wear resistance of the bainitic steels depends on the volume fractions of hard phases, carbide and martensite-austenite phase, for rolling-sliding as well as other types of dry-wear loading. Pearlite performs exceptionally well under rolling-sliding conditions since the lamellar microstructure is modified so as to present a greater area fraction of hard carbide plates at the wear surface, a fraction in excess of the bulk volume fraction of carbide. Recommendations are made for the application of these steels in rolling-sliding and other dry-wear circumstances.