Powder Metallurgy Alloys Research Articles

Hot deformation behavior and processing workability of a powder forged Fe-2.1Cu-0.5C alloy

Hot deformation behavior of as-sintered Fe-2.1Cu-0.5C alloy was evaluated through the construction of constitutive equations and a hot processing map. The hot deformation behavior was investigated at different temperatures and strain rates and microstructure observations were subsequently conducted. Flow stress for the initiation of dynamic recrystallization mechanism was determined. Tensile and fatigue strength tests were conducted at room temperature. It was observed that the microstructure of the alloy forged at lower temperature exhibited smaller grain size and its grain size increased with higher forging temperatures. Mechanical testing results revealed that an increase in the forging temperature led to a lower tensile strength and a higher fatigue strength. This change can be attributed to the larger grain sizes and the reduction of microcracks. A forging temperature at 1050 °C was recommended to achieve optimal mechanical properties for powder forged Fe-2.1Cu-0.5C products. These results might give some hints for optimizing process conditions and improving mechanical properties of powder metallurgy alloys by the use of constitutive equations and thermal processing maps.

FEM and machine learning aided modelling of compressive deformation anisotropy in pressure-less sintered Cu-15Ni-8Sn alloy

Pressure-less sintering integrated forging is an effective method for densification enhancement of powder metallurgy (PM) processed Cu-15Ni-8Sn alloy. Nevertheless, compressive deformation anisotropy associated with uniaxial forging creates heterogeneous deformation zones containing residual porosity, resulting in strength degradation of the PM alloy. This work introduces a novel approach for mitigating the anisotropy arising from forging by characterising the compressive deformation heterogeneity using a synergy of finite element method (FEM) and machine learning (ML) approaches. Results obtained from Gurson model-based FEM simulation of uniaxial forging process indicate that decreasing the aspect ratio (AR) of sintered preform leads to reduction in plastic deformation heterogeneity. Additionally, the semi supervised ML framework developed here unravels three distinct strain hardening regimes and predicts an upward paradigm shift in the quantitative distribution of instantaneous strain hardening exponent with the decrease in AR. These computational predictions align with the experimental forging results which demonstrate substantial enhancement in strain hardenability, formability and densification of lower AR preform due to more uniform deformation. Uniaxially forged compact depicted a notable increase of 14 % in relative density along with significant improvement in hardness by 66 % as compared to the sintered compact, which can be attributed to forging induced pore elimination at microstructural level. The promising results obtained in this study have practical implications in the development of sustainable green manufacturing technology to produce high strength porosity tailored Cu-15Ni-8Sn alloy.

New Method for Microstructure Segmentation and Automatic Grain Size Determination Using Computer Vision Technology during the Hot Deformation of an Al-Zn-Mg Powder Metallurgy Alloy

New Method for Microstructure Segmentation and Automatic Grain Size Determination Using Computer Vision Technology during the Hot Deformation of an Al-Zn-Mg Powder Metallurgy Alloy

Overcoming optical image challenges in automatic grain size measurement using a novel computer vision algorithm applied to hot deformation of Al-Zn-Mg Powder metallurgy alloy

The present study introduces a novel approach that utilizes the Python programming language along with the OpenCV, SciPy, and NumPy libraries. This approach addresses challenges related to grain size measurement in optical images, including issues such as fused grains caused by fragmented boundaries, noise resulting from lens aberrations, and grains located at the image edges. These challenges have been successfully overcome, enabling the segmentation of microstructures and the automated determination of grain characteristics, including grain counting, ASTM grain size, and grain size in µm. The developed algorithm was validated using optical images obtained after hot deformation, and a comparative analysis was performed with manual measurements. The results showed an average absolute relative error (AARE) of 3.1% for the number of grains, 0.19% for ASTM grain size, and 1.59% for grain size in µm, with an R-value of 0.999.

Surface Modification of Ti-Nb Alloy in Alkaline Solution to Enhance Bioactivity

Titanium alloys, especially titanium-niobium alloy have been reported as a potential biomaterial with good biocompatibility and non-toxicity. However, there is a lack of studies in alkaline surface treatment of new beta titanium alloy fabricated by vacuum arc melting (VAM) and powder metallurgy (PM) technique with high addition of niobium percentage. The purpose of this research was to examine the feasibility of surface modification on new beta Ti-40wt% Nb alloy in sodium hydroxide solution in order to form bioactive alkaline titanate layer. The characterization involved in this study is X-ray diffraction analysis (XRD), scanning electron microscope (SEM), microhardness, density measurement and optical microscope (OM). Development of amorphous alkaline titanate layer consisted of titanium hydrate, sodium titanate and oxide mixture of titanium oxide, niobium, niobium oxide were revealed by XRD. SEM shows titanate hydrogel layer form on Ti alloy PM thicker than on Ti alloy VAM. Microhardness and density measurement for Ti alloy VAM is greater than Ti alloy PM. OM shows porous surface on Ti alloy PM compare to VAM. This research suggests that the formation of sodium titanate layer on the surface of Ti-Nb alloy enhance bioactivity with better osteointegration and present higher formation of apatite which is crucial for the desired biomedical implant.

Investigating the effects of deformation-induced densification on the constitutive behavior and corrosion resistance of Al–Zn–Mg powder metallurgy alloy during hot deformation

The electrochemical behavior is most strongly influenced by deformation, which may either accelerate or decelerate failure during service. Therefore, in the present study, the Al–5.6Zn–2Mg alloy fabricated by powder metallurgy was subjected to hot deformation at various temperatures (300–500 °C) and strain rates (0.5–0.005 s−1) on a hydraulic press, and then, the effect of deformation-induced densification on corrosion behavior was studied using electrochemical corrosion tests. Flow stress is mathematically modeled using the strain-compensated Arrhenius model. The model developed was reliable to predict, with an average absolute relative error (AARE) of 3.16% and an R2 value of 0.98. The potentiodynamic polarization results showed that as the degree of porosity in a sintered sample is reduced, there was a decrease in the corrosion current density and an increase in the pitting potential. Al–5.6Zn–2Mg corrosion resistance significantly improved with deformation temperature, whereas strain rates decrease it, due to a decrease in pore content. Icorr of 2.4982 µA/cm2 and Epit of 0.876 V have been found for the highly deformed preforms under 500 °C and 0.005 s−1 strain rate condition. EIS results showed a high contact resistance of 2659 Ohm·cm2 and high hardness value of 113.12 Hv for the preform deformed under 500 °C and 0.005 s−1 strain rate. The reduction in porosity, decrease in active surface area after the deformation process, densification behavior, and hardness are all related to the electrochemical behavior. Pitting corrosion was observed in deformed preforms as a corrosion mechanism; the dynamic recovery feature is observed from the flow behavior.

The effect of plastic strain and temperature on the corrosion resistance of the Al-5.6Zn-2Mg powder metallurgy alloy during hot upsetting

Failure may be expedited or slowed down depending on the way the plastic strain interacts with the corrosive media. Therefore, in the present study, the Al-5.6Zn-2Mg alloy produced by the powder metallurgy process was subjected to hot deformation at different plastic strain levels and temperatures (300 °C–500 °C) on a hydraulic press, and then the impact on Corrosion susceptibility was studied using electrochemical corrosion tests in a 3.5% NaCl solution at room temperature. The results of potentiodynamic polarization showed that as deformation levels increased, the corrosion current density decreased and the pitting potential increased. The corrosion resistance of Al-5.6Zn-2Mg increased considerably with an increase in upsetting temperature, due to increasing grain size and a decrease in pore content. Icorr of 2.4982 (μA cm−2) and Epit −0.876 V have been found for the highly deformed preforms under 500 °C condition. EIS results showed a high contact resistance of 2659 Ohm.cm2 for the sample deformed under 500 °C. After the deformation process, densification behaviour is related to the electrochemical behaviour. Pitting corrosion occurred in all deformed samples, while intergranular corrosion was found only in the severely deformed samples.

Microstructure transformation and pore formation mechanism of Mo-14Re alloy weld by vacuum electron beam welding

The vacuum electron beam welding (EBW) properties of Mo-14Re alloys were studied in this work. The weld morphology and microstructure were observed by optical microscope (OM) and scanning electron microscope (SEM). By using 3D Measuring Laser Microscope, energy dispersive spectroscopy (EDS), electronic probe micro analysis (EPMA) and transmission electron microscope (TEM), the weld pore was further characterized. In addition, its formation mechanism was analyzed. The results showed that the grains in fusion zone (FZ) of the powder metallurgy (PM) alloy weld obviously grew up to about 226.6 ± 75.7 μm and there were a large number of 12∼80 μm spherical pores. The element oxygen was enriched in the pores and a layer of MoO2 was formed on the surface. The formation of pores may be closely related to the micropores and high oxygen content in the materials. Under the strong stirring of the molten pool, the generated carbon monoxide (CO) and molybdenum monoxide (MoO) bubbles couldn't escape and remained in the weld to form pores. However, no pores were found in the melted alloy weld. It was difficult to generate bubbles by homogeneous nucleation for the melted alloy. Due to the grain coarsening, the microhardness value of the weld significantly decreased.

The mechanical properties of austempered 1.75Ni-1.5Cu-0.5Mo alloyed PM steels

The effects of isothermal annealing on the microstructure and mechanical properties of ferrous based Ni-Cu-Mo-C diffusion alloy powder metallurgy (PM) components were investigated. For this purpose, the powder mixtures were pressed and sintered at 1150 °C. After full austenitisation at 825°C, they were kept isothermally in a neutral salt bath at 450°C for 15–120 min. Microhardness (HV 0.01), tensile and impact toughness tests of the samples were carried out at room temperature. The hardness value decreased with increasing austempering time. As a result of the austempering of 120 min, the tensile strength increased by 12.2% and became 460 MPa compared to the heat treatment period of 15 min, and the impact toughness was determined to be 14.3 j.cm−2 with an increase of 21%. Under the conditions in this experimental study, optimum strength and ductility values were obtained with austempering time applied in the range of 90–120 min.

Effect of vibration and cutting zone temperature on surface topography during hybrid cooling/lubrication assisted machining of Vanadis 10

Abstract New alloy materials developed to meet the increasing technological needs of people come into our lives with some difficulties in terms of machinability. New cooling and lubrication techniques have been developed to facilitate the workability of such difficult-to-process materials and protect the world ecologically and the quality of the produced product. The workpiece used in this study, Vanadis 10 SuperClean, is a high vanadium alloyed powder metallurgy tool steel offering a unique combination of excellent abrasive wear resistance in combination with a good chipping resistance. The present study investigated the effects of dry, cryo, and CryoMQL cutting conditions on cutting tool vibration amplitude, cutting temperature, surface roughness, tool wear, and tool life in turning of Vanadis 10 tool steel used in the automotive industry. The experiments were performed using TiCN/Al2O3/TiN coated cemented carbide tools and cutting parameters as the constant depth of cut (1 mm), feed rates (0.08, 0.1, 0.12 mm rev−1), and cutting speeds (80, 100, 120 m min−1). The results obtained from experiments showed that spraying liquid nitrogen into the cutting zone provided significant improvements on cutting temperature, tool wear, cutting tool vibration amplitude, and surface roughness. The best results in terms of all output were achieved in the CryoMQL cutting environment. CryoMQL environment has reduced surface roughness up to 65.03 %, flank wear 56.99 %, cutting temperature 32.77 %, and cutting tool vibration amplitude up to 42.76 % compared to dry machining.

Effects of thermal cracks on friction and wear properties of forged steel used in railway brake discs

In this study, the effects of thermal cracks on the friction and wear properties of forged steel used in railway brake discs were investigated. First, friction tests were conducted on forged steel obtained from a serviced brake disc with and without thermal cracks against powder metallurgy alloys obtained from brake pads. The occurrence of thermal cracks reduced the coefficients of friction (COF) to one-third of that of the specimen without thermal cracks and sharply increased the fluctuation of the COF. The observation of the third-body film (TBF) indicated that its integrity was destroyed by thermal cracks; the TBF on the thermal crack was discontinuous and island-like, surrounded by adhesion pits. The poor quality of the TBF was responsible for the low and fluctuating COF of the specimen with thermal cracks. The debris tended to fill the interspaces of the thermal cracks instead of forming a TBF owing to the occurrence of thermal cracks, while the compressional force was not large enough to cause the accumulation and compaction of the debris to form an integrated TBF.

Influence of incremental pre-strain on corrosion behavior of Al-Zn-Mg powder metallurgy alloy during hot forging

The interaction of pre-strain and corrosive medium can either accelerate or decelerate material failure. In the present study, the electrochemical activity of forged preforms is assessed by the open circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). A powder metallurgy route was used to fabricate Al-5.6Zn-2Mg alloy with 0.8 relative density. The fabricated alloy was subjected to hot axial forging at various temperatures such as 300°C, 400°C, and 500°C under a 0.005/s strain rate. The microstructure and corrosion morphologies of sintered and forged preforms under various deformation levels and temperatures were investigated using scanning electron microscopy (SEM). After the deformation process, flow behavior, densification behavior, and electrochemical behavior are studied. Deformation behavior (true strain was linked to the local mechanical properties (hardness) and electrochemical properties (pitting potential (Epit)). The potentiodynamic polarization results showed that as the degree of deformation increased, there was a decrease in the corrosion current density and an increase in the pitting potential. Al-5.6Zn-2Mg corrosion resistance significantly improved with a degree of deformation and temperature. A mathematical model relating corrosion rate and true strain for various deformation temperatures is developed to estimate the corrosion rate for any true strain. Pitting corrosion was observed in deformed preforms as a corrosion mechanism. Because of the increased deformation degree and temperature, the corrosion morphologies showed the closing of pores.

The Investigation on Dimensional Stability in Some Sintered Powder Metallurgy Alloys

The subject of this research was to study the effect of sintering time on the dimensional characteristics of some powder metallurgy (PM) materials. The powders used in this study are prealloyed iron-based powders with Cu, Ni and Mo. The powders were single pressed at 600 MPa and the disc specimens have the dimensions of 8-6 mm. The green compacts were sintering in a laboratory furnace at 1150 ºC for 60, 75 and 90 minutes and air-cooled to room temperature. The density of green and sintered specimens, the porosity and the dimensional changes were evaluated.

The relationship between grain size distribution and ductile to brittle transition temperature in FeCrAl alloys

A FeCrAl (Fe12Cr6Al2Mo) alloy was prepared by two methods, (a) traditional wrought and (b) powder metallurgy (PM). Both alloys exhibited the same average grain size (∼40 um), but the PM alloy displayed a wider grain size distribution. Charpy impact testing showed that the ductile to brittle transition temperature width is dependent on the grain size distribution width.

Oxidation behavior in static air and its effect on tensile properties of a powder metallurgy EP962NP nickel-based superalloy

Oxidation behavior and its effect on tensile properties of a powder metallurgy EP962NP superalloy have been investigated. Results show that the oxidation resistance of studied alloy has been improved by hot isostatic pressing as compared to the as-cast one. Oxidation process of the alloy powder metallurgy EP962NP is limited by diffusion of Cr3+ due to oxidation activation energy of 244.1 kJ·mol−1. In addition, the main reason for cracking and spalling during steady-state oxidation can be inferred as the rapid increase in growth stress caused by spinel. Interestingly, the tensile samples oxidized at 900 °C exhibit improved plasticity due to the refinement of γ′ caused by octet splitting.

(Digital Presentation) On the Effect of Sizing on Electrochemical Response and Localized Corrosion Behavior of Alumix 123 P/M Alloy

Powder metallurgy (PM) as an additive technique for fabricating parts has been used by many industries such as automotive, aerospace, and medical. However, it has been centered mostly around automotive industry which has benefited from large volume production, low cost, and near-net-shape manufacturing that comes with PM. High demand for producing fuel-efficient and light vehicles in automotive industry provides a driving force for extensive research activity on PM of aluminum alloys. Among different aluminum alloys, PM of 2xxx series are among the best choices due to their good sinterability and mechanical response. But industrial PM parts need post processing treatments such as sizing to meet the real-world applications. While sizing is widely used in industry to provide tighter tolerance, it can also help improving density, fatigue behavior, yield strength, and hardness. But there were very few studies on the effect of sizing on electrochemical response. In this study we produced Alumix 123 PM alloy using a press-and-sinter process and then sizing was applied on some of the samples to compare their long-term electrochemical behavior. The changes in the surface profile and roughness of the samples were investigated using confocal laser scanning microscopy. Electrochemical impedance spectroscopy (EIS) as a powerful technique for investigating long-term electrochemical behavior has been used to find the effect of sizing on corrosion response of Alumix 123 PM. In addition, effect of sizing on localized corrosion and pitting tendency was thoroughly discussed using electrochemical polarization results, scanning electron microscope images, and EIS outcomes.

Effect of ball milling on NiTi powder metallurgy alloy

Mechanical alloying, especially nickel-titanium alloys, has attracted great interest recently as researchers strive to enhance the properties of nanocomposites, expand their usefulness, and how to produce them at minimal costs and produce homogeneous fine powders.In this paper, high-energy ball milling was used to produce Ti-Ni ultrafine powders. The effects of grinding parameters such as grinding tools and initial state of powders, grinding conditions such as operating times, in addition to the effect of equal size balls and the speed of the grinding machine, were investigated, while avoiding contamination of the powders in contact with air by applying silica. Milling process balls such as X-ray diffraction, SEM, EDS, plus particle size.

Turning/Shot peening of Nickel-based powder metallurgy superalloy: Effect on surface integrity and high-temperature low-cycle fatigue properties

In this study, a nickel-based powder metallurgy alloy was processed via turning, ceramic bead peening, and shot peening by high-intensity cast-iron shots and low-intensity ceramic beads (denoted as compound shot peening). We investigated the surface morphology (surface stress concentration factor, Kst), the surface residual stress profile, microstructure, and the hardness gradient of three surface states and compared the high-temperature low-cycle fatigue lives. The results showed that the surface stress concentration coefficients after turning, ceramic bead peening, and compound shot peening were 2.39, 1.98, and 2.12, respectively. The average surface roughness, Sa, after turning was low, but the bottom of the tool mark was sharp, so the Kst value was higher than that after shot peening, which formed a round bottom by bead blasting. Compared with ceramic bead peening, a surface structure with a deeper compressive residual stress profile and a higher hardness gradient was formed after compound shot peening, and nanostructured features appeared on the outermost surface. The estimated low-cycle fatigue lives after the ceramic bead peening and compound shot peening were 0.99 and 3.13 times longer than after the turning process respectively with strain amplitude 0.5% at 538℃. Moreover the gain of compound shot peening on low cycle fatigue performance gradually decreases with the increase of the strain amplitude.

Effect of Alloying Elements on Strengthening Phase and Solidification Structure of Ti-Al-Mo-Zr Titanium Alloy

This paper mainly studies the composition of strengthening phase, characteristic precipitation temperature and composition range of strengthening phase in Ti-Al-Mo-Zr-Si medical titanium alloy, and the influence of element changes on the content and microstructure of strengthening phase. Promote the formulation of thermodynamic process of titanium alloy powder metallurgy, as well as the formulation of alloy hot working and solid solution aging process. In this paper, Panda thermodynamic software is used to calculate the multicomponent alloy thermodynamics and multicomponent phase diagram of titanium alloy materials. The effects of Al, Mo, Zr, Si and other elements on the precipitation of strengthening phase and the phase transformation content of solidification structure were obtained. It is found that the content of Mo is more than 2 wt.% β phase transition precipitation angle. Meanwhile, in order to avoid the excess of precipitates such as Mo5Si3 and M3Si, the content of Mo should be less than 4.6 wt.%. The content of Zr can be maintained at about 1.5 wt.%. If the aging precipitation of the material is considered, it can be controlled to be less than 2 wt.%. The content of this paper is the basis and improvement of titanium powder metallurgy technology and rapid prototyping technology.

Workability and corrosion behavior studies on sintered iron‐based hybrid powder metallurgy alloys

AbstractSintered low carbon steels are developed using prealloyed and elemental powders to improve the mechanical properties of powder metallurgy and powder forged parts. The research focuses on the mechanism of workability and corrosion studies on sintered preforms of Alloy 1 (ATOMET4601 + 0.35%C) and Alloy 2 (ATOMET4601‐0.35%C‐0.25%Mn‐0.1%Si‐0.9%Cr). Sintered preforms of relative densities of 81%, 84%, and 90% were used for the present work. The preforms with 84% relative density have been used to study the formability parameters. It is observed from the experimental study that the Alloy 2 preforms with the addition of alloying elements have undergone lesser densification and deformation due to the work hardening mechanism. Corrosion studies have been carried out by conducting aqueous immersion and electrochemical corrosion tests on these two alloys using 18% HCl solution at different timings. It is found that the Alloy 2 has exhibited a better corrosion resistance than the Alloy 1 due to the addition of various alloying elements. It is also observed that the corrosion rate has decreased with an increase in densification irrespective of the alloys. The microstructures, scanning electron microscopy, and X‐ray diffraction of corroded surfaces have been corroborated with densification and the corrosion behavior of alloys.