Alloy Samples Research Articles

An EBSD analysis of a commercial immiscible Cu43%Cr alloy after high-pressure torsion processing and annealing

ABSTRACT The influence of high-pressure torsion (HPT) and annealing on microstructure, texture and thermal stability of an immiscible composite Cu43%Cr alloy was studied using electron backscatter diffraction, X-ray diffraction and microhardness measurements. As-received alloy samples were subjected to HPT and subsequent annealing treatment in the range of 210–850°C for 1 h in order to develop ultrafine-grained (UFG) microstructures and highlight their thermal stability. The Cu and Cr grains were refined to ∼0.45 and ∼0.39 µm, respectively and exhibited equiaxed morphology. The crystallographic texture was of shear type in both Cu and Cr with the domination of C and F orientations, respectively. The UFG microstructure and texture were retained in the Cu43%Cr alloy up to 850°C. The global results show that the immiscible composite Cu43%Cr alloy exhibits a high thermal stability up to 850°C. The evolution of the microstructure, texture and thermal stability of the UFG Cu43%Cr alloy was compared to published data and available models.

Multiple strengthening mechanisms of grain/twin boundaries, dislocations and nanoprecipitates in Mg alloys induced by laser shock processing

To investigate the strengthening mechanism for magnesium alloy with gradient nanostructures, magnesium alloy AZ31 with a varying volume fraction of nano gradient structure layers was obtained by using laser shock processing technology and setting parameters such as laser energy and spot size. Macro loading tests for uniaxial tensile and uniaxial compression were carried out, and a microhardness test, metallographic test, and Scanning observations by transmission electron microscope(TEM) and scanning electron microscope(SEM) were carried out. The results show that the tensile and compressive yield strength of the magnesium alloy samples and the microhardness of the matrix are significantly improved, and the volume fraction of the gradient layer has a significant impact on the macromechanical properties. The microstructure of the sample shows abundant grain boundaries(GBs) and twin boundaries(TBs), various dislocation forms, and nanoprecipitates that are dispersed in the crystal. The structural characteristics show that a variety of microstructures exist in a gradient along the thickness direction. The comprehensive analysis shows that the improvement in the macromechanical properties of magnesium alloy samples is the comprehensive result of multiple strengthening, such as grain refinement strengthening, high dislocation density strengthening and nanoprecipitate strengthening.

INVESTIGATION OF MICROSTRUCTURE OF AA7075 ALLOYS AFTER SEVERE PLASTIC DEFORMATION APPLICATION

The aim of this study is to investigate the change of microstructural properties of AA7075 alloys after severe plastic deformation. Severe Plastic Deformation is a process used to improve the properties of the material by creating intense plastic deformations on the material surface. Equal channel angular compression molding (ECAP) was used for the severe plastic deformation process in our study. AA7075 alloy samples were primarily prepared for severe plastic deformation treatment. Then, the microstructural properties of the samples were investigated using various imaging techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The research results showed that significant microstructural changes occurred in AA7075 alloys after the severe plastic deformation process. The SPD process improved the mechanical properties of the material by transforming the crystalline structures of the material into a fine-grained structure. In addition, it was observed that deformation lines and pits occurred on the surface of the samples after the SPD process. It is seen that the SPD treatment increases the mechanical properties of the material such as strength, hardness and durability. Therefore, this study is an important step towards the development of the alloy's use in various industries.

ANALYSIS OF ADDITIVELY MANUFACTURED AlSi10Mg ALLOY USING X-RAY DIFFRACTION

This research deals with the study of additively manufactured AlSi10Mg alloy samples by X-ray diffraction. The effect of sample orientation during 3D printing by Selective Laser Melting on the values of macroscopic residual stresses and microstructural parameters and their possible inhomogeneities of the cylindrical sample was investigated. Phase analysis identified the intermetallic phase Mg2Si in addition to the major phases (solid solutions of Al and Si). Tensile residual stresses weredetected in the surface layer for all samples. Inhomogeneities of the investigated parameters of all samples were observed along the circumference of the shank. These effects may be related to the direction of the layers relative to the axis of the sample. These inhomogeneities form so-called microstructural notches or weak spots that are prone to the formation of fatigue cracks, which have a major influence on the fatigue life.

Micro X-ray fluorescence (μ-XRF) methodology for quantitative elemental imaging of Al–Zn–Mg–Cu alloys with varying chemical compositions

The preparation and characterization of Al–Zn–Mg–Cu alloys with varying chemical compositions are helpful for rapid screening of the optimal compositions in the research and development of new materials. The traditional testing methods cannot accurately determine the composition gradient in samples because they have a low spatial resolution or are semi-quantitative and time-consuming. The micro X-ray fluorescence (μ-XRF) methodology has been used for the elemental imaging of Al–Zn–Mg–Cu alloys with varying chemical compositions. The experimental conditions, including testing voltages, testing currents and the dwell time for each pixel, were optimized systematically to improve the repeatability and accuracy of the μ-XRF methodology. The quantitative elemental imaging of an Al–Zn–Mg–Cu alloy rod sample using μ-XRF was performed, and the results were validated by conducting spark optical emission spectroscopy. The limits of detection of μ-XRF for Zn, Mg, and Cu were 0.007 wt%, 0.068 wt%, and 0.002 wt%, respectively. This versatile elemental imaging technique provided an effective means for the component analysis and process evaluation of alloy samples with a composition gradient and thus for research and development of new materials.

Influence of process parameters on the quality of powder bed fusion-fabricated Ni-Co-Fe-Mn-Ti high entropy alloy prints using elemental powders

Ni-Co-Fe-Mn-Ti high entropy alloys (HEA) were fabricated via powder bed fusion using elemental powders. Based on thermodynamic calculations, 3 alloys were designed with medium to high entropy (from 3 to 5 components) and printed. Additive manufacturing (AM) was performed, while varying the laser power and exposure time (point-by-point exposure laser working mode). The obtained samples were characterised by means of macroscopic observations combined with porosity analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), as well as compression and hardness tests. The varied process parameters and the content of individual alloying elements directly impacted alloy processability and sample properties. We proved that it is possible to produce HEAs (Ni-Co-Fe-Mn-Ti) with low porosity and good chemical homogeneity from elemental powders. By comparing the processes of producing 3-, 4-, and 5-component alloys, it was observed that it is not the quantity of the components but the melting temperatures of the individual elemental powders and their tendency to oxidise that affect obtaining good 3D prints. The most promising results for 5-component HEAs were obtained for 145 µs of laser exposure time combined with laser powers of 250 and 300 W.

Production and Characterization of Ta-Sn Alloy Foam for Biomedical Applications

In this study, Ta-Sn alloy foam was manufactured by using space holder method for biomedical applications. The aim of the study is development of an alloy with suitable mechanical properties, with good medical imaging (digital radiography, computed tomography) properties (radiopacity), with high bioactivity. Powder metallurgy-based space holder method enables manufacturing of open-cell foam with low elastic modulus. Powder mixtures were prepared by mechanical alloying. Carbamide was used as a pore former. Ta has suitable radiopacity, strength, ductility, corrosion resistance and biocompatibility. But Ta has high price, high melting temperature, high activity, and high density. Sn addition was lowered the melting temperature, and cost of Ta. Sinterability of Ta, which is a refractory metal, was enhanced by Sn addition. Corrosion behaviour of Ta alloy was examined. Young’s modulus was determined by compression and ultrasonic tests. Increasing Sn content of the alloy increased the Young’s modulus. Increasing porosity decreased the Young’s modulus. Ta alloy has no cytotoxic potential according to neutral red test. Sn addition was lowered the polarization resistance and slightly increased the corrosion rate of Ta-Sn alloy samples.

Simultaneously enhanced tensile strength and ductility of nano-Y2O3-reinforced TiAl alloy prepared by directed energy deposition

The effect of Y2O3 nanoparticles on microstructure and high-temperature mechanical properties of Ti–48Al–2Cr–2Nb alloy prepared by directed energy deposition was investigated. Cracks in the TiAl alloy sample were eliminated by a new directed energy deposition method with a preheating unit. The results indicated that the microstructure of TiAl alloy without Y2O3 nanoparticles addition was composed primarily of (α2/γ) lamellar colony. While the equiaxed γ phase was generated within the (α2/γ) lamellar colony and on the colony boundaries, and the microstructure exhibited a duplex structure due to the 0.5 wt% nano-Y2O3 addition, and the grain size was decreased from 183 μm to 25 μm. The ultimate tensile strength and fracture elongation tested at 750 °C were enhanced simultaneously from 615.1 to 805.7 MPa and from 5.56% to 7.40%, respectively, by 0.5 wt% Y2O3 nanoparticles addition. Finally, the strengthening mechanism and microstructure refinement mechanism were discussed in detail. This investigation provides a valuable reference for TiAl alloy fabrication and widespread engineering applications.

Numerical and experimental study of RHEAs surface morphology and defect in selective laser melting

Refractory high-entropy alloys (RHEAs) are a new category of high-temperature materials that are high-entropy alloys with refractory metal elements as the major components. SLM technique provides distinct benefits in preparing refractory metals with high melting points. The effects of laser power and scanning speed on the surface morphology and internal defects of VNbMoTaW RHEAs samples were examined using numerical and experimental methods. A DEM-CFD model was created to simulate the process of SLM producing a single-layer, single-track model. The simulation findings show that the melt pool's channel width is 62.31 μm at a scanning speed of 300 mm/s and a laser power of 150 W. The channel width grows to 96.92 μm when the laser power rises to 450 W. When the laser power is increased, the channel becomes flatter. To prepare the VNbMoTaW samples, the process parameters with the highest quality in the numerical simulation were chosen. At a scanning speed of 300 mm/s and a laser power of 450 W, the measured channel width of the high-entropy alloy samples is approximately 104.13 m. Similarly to the numerical simulation results, the channel width of the models generated at the same scanning speed increases as the laser power increases. At low laser power, it was discovered that many unmelted powder particles were dispersed on the surface of the samples. The primary defects found in the samples were pores and fractures. The interlayer non-melting cracks on the sample cross-section vanish at elevated laser power. Whereas the quality of samples created at low scanning speeds is higher at the same laser power, the quality of samples declines as the scanning speed of the laser increases.

Structural and mechanical evaluation of a new Ti-Nb-Mo alloy produced by high-energy ball milling with variable milling time for biomedical applications

The main focus of this work is to investigate the impact of varying milling times (2 to 18 h) on the structural and mechanical properties of the developed Ti-Nb-Mo alloy. The morphology, phase composition, microstructure, and mechanical behavior of milled and sintered Ti-25Nb-25Mo alloy samples were characterized systematically using x-ray diffraction, scanning electron microscope, optical microscope, and Vicker microhardness. It was noted that the quantity of the β-Ti phase increased as the milling time increased. After 12 h of milling, the synthesized alloys exhibited a spherical morphology and texture with homogeneous distribution. The milled alloys' structural evolution and morphological changes were found to be dependent on their milling duration. Morphological analysis revealed that the crystallite size and mean pore size decreased when the milling duration increased, reaching minimum values of 51 nm and < 1 μm, after 12 and 18 h respectively. As the milling time increased, the grain size decreased, resulting in an increase in density, microhardness, and elastic modulus. Ti-25Nb-25Mo will presents good anti-wear ability and higher resistance to plastic deformation due to enhanced mechanical characteristics (H/E, and H3/E2). Hence, the developed Ti-25Nb-25Mo alloys with reduced elastic modulus and desirable mechanical properties were found to be a promising option for biomedical applications.

Enhancement of surface characteristics of additively manufactured γ-TiAl and IN939 alloys after laser shock processing

The enhancement in laser technology opened up new methods such as additive manufacturing (AM) of metals. While AM offers high design flexibility and reduced material usage, it can also produce problematic parts due to poor surface quality. A variety of post-processing techniques are available to address the drawbacks associated with the surface properties of AM. Laser Shock Processing (LSP) is one of the unique methods that induces compressive residual stress (CRS) on the surface and subsurface by creating severe plastic deformation. In this study, two critical aerospace alloys (γ-TiAl and IN939) were manufactured through two different methods called Powder Bed Fusion with Electron Beam (PBF-EB) and Powder Bed Fusion with Laser Beam (PBF-LB). Subsequently, AM samples were investigated to observe single layer LSP effects on the surface. The results of the laser peening process were determined by residual stress, microhardness and surface roughness measurements. The residual stress profiles showed that LSP significantly induces CRS on the surfaces of AM alloys. For the γ-TiAl and IN939 samples, the maximum values of CRS and depth of CRS were −460 MPa/1000 µm and −516 MPa/700 µm, respectively. Similarly, the microhardness of the materials was increased by 44.4 % for γ-TiAl and 18.2 % for IN939 by laser post-processing. In addition, a comparison of the roughness of the unground and ground AM samples was carried out. Depending on the surface condition of the AM samples, LSP had different outcomes. For example, the extreme roughness of the AM samples was partially reduced by the thermal effects of the high-energy laser shots. When comparing the roughness values in terms of Ra and Rz, there were decreases in the range of 14.7–21.3 % and 3.34–39.3 % for unground IN939 samples. However, for unground γ-TiAl samples, depending on the direction of measurement, roughness variations were observed as a 0.99 % decrease − 5.3 % increase for Ra and a 2.2 % decrease − 14.2 % increase for Rz. The roughness values for ground samples of both alloys were drastically increased, varying between 42.1 % and 7x increase. Sa values were recorded on unground AM samples. For IN939 and γ-TiAl samples these values decreased by 8.41 % and 15.8 % respectively.

A case study of hybrid manufacturing of a Ti-6Al-4V titanium alloy hip prosthesis

Hybrid manufacturing (HM) is a process that combines additive manufacturing (AM) and subtractive manufacturing (SM). It is becoming increasingly recognized as a solution capable of producing components of high geometric complexity, while at the same time ensuring the quality of the surface finish, rigour and geometric tolerance on functional surfaces. This work aims to study the surface finish quality of an orthopaedic hip resurfacing prosthesis obtained by HM. For this purpose, test samples of titanium alloy Ti-6Al-4V using two Power Bed Fusion (PBF) processes were manufactured, which were finished by turning and 5-axis milling. It was verified that, upon the machining tests, no differences in Ra and Rt were found between the various types of AM. Regarding the type of SM used, 5-axis milling provided lower roughness results with a consistent value of Ra = 0.6 µm. The use of segmented circle mills in 5-axis milling proved to be an asset in achieving a good surface finish. This work successfully validated the concept of HM to produce a medical device, namely, an orthopaedic hip prosthesis.As far as surface quality is concerned, it could be concluded that the optimal solution for this case study is 5-axis milling.

In Vitro Studies Regarding the Effect of Cellulose Acetate-Based Composite Coatings on the Functional Properties of the Biodegradable Mg3Nd Alloys.

Magnesium (Mg) alloys are adequate materials for orthopedic and maxilo-facial implants due to their biocompatibility, good mechanical properties closely related to the hard tissues, and processability. Their main drawbacks are the high-speed corrosion process and hydrogen release. In order to improve corrosion and mechanical properties, the Mg matrix can be strengthened through alloying elements with high temperature-dependent solubility materials. Rare earth elements (RE) contribute to mechanical properties and degradation improvement. Another possibility to reduce the corrosion rate of Mg-based alloys was demonstrated to be the different types of coatings (bioceramics, polymers, and composites) applied on their surface. The present investigation is related to the coating of two Mg-based alloys from the system Mg3Nd (Mg-Nd-Y-Zr-Zn) with polymeric-based composite coatings made from cellulose acetate (CA) combined with two fillers, respectively hydroxyapatite (HAp) and Mg particles. The main functions of the coatings are to reduce the biodegradation rate and to modify the surface properties in order to increase osteointegration. Firstly, the microstructural features of the experimental Mg3Nd alloys were revealed by optical microscopy and scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy. Apart from the surface morphology revealed by SEM, the roughness and wettability of all experimental samples were evaluated. The corrosion behavior of the uncoated and coated samples of both Mg3Nd alloys was investigated by immersion testing and electrochemical testing using Simulated Body Fluid as the medium. The complex in vitro research performed highlights that the composite coating based on CA with HAp particles exhibited the best protective effect for both Mg3Nd alloys.

Influence of PbCl2 and KCl salt mixture on high temperature corrosion of alloy 625

Aggressive corrosion can occur when firing waste or bio-based fuels, due to the presence of high concentrations of heavy metals, alkali metals, and chlorides. These deleterious compounds deposit on furnace walls and can form mixtures that can rapidly accelerate corrosion. The effect of salts containing lead had not been studied extensively at temperatures lower than 400 °C in nickel-based materials. This study investigates the effect of the individual salts PbCl2 and KCl and their mixture on the high temperature corrosion of alloy 625 at 340 °C and 380 °C. Samples of alloy 625 were covered with individual salts or a salt mixture and exposed to high temperatures in an atmosphere of synthetic air, 20-vol% H2O, and 100 ppm HCl. The results show that the presence of individual salts does not induce observable corrosion attack on alloy 625 after 168 h at any tested temperature. The salt mixture did cause a severe corrosion attack at 380 °C, observed after 24 h of exposure. It is suggested that the salt mixture induces the formation of lead chromates that may prevent or disrupt the formation of a protective chromia scale. It is believed that a key part of the mechanism is the formation of eutectic melts by the interaction of the scale with the salt mixture. Thermodynamic equilibria calculations show that the first melting temperature of PbCl2 and KCl salt mixture after reaction with oxygen can be as low as about 382 °C, and even lower (357 °C) if chromates are present.

Unraveling the role of sintering temperature on physical, structural and tribological characteristics of ball milled Co28Cr6Mo biomaterial based alloy

This work aim to investigate the effect of sintering temperature (950–1250 °C) on structural, physical, tribological properties of nanobiomaterial Co28Cr6Mo alloy for total hip prosthesis obtained by high Energy ball milled. Several techniques such as density, porosity, microhardness, and Young’s modulus were used to assess the mechanical and physical characteristics. Tribological behavior were conducted using a ball-on-plate type Oscillating tribometer, under different applied loads (2, 10 and 20 N), under a wet condition using hank’s solution to simulate human body fluid. SEM, EDS and XRD analysis results, showed that Co-Cr-Mo alloy samples sintered exhibit the same phases created by the Co element. The alloy sintered at 1250 °C displayed the highest micro-hardness value in terms of mechanical characteristics (386.75 HV0.1. The porosity changes from 17% to 10% and endorse a higher change in Young’s modulus around 61.84 and 92.5 GPa for samples sintered beteewn 950 and 1250 °C, respectively,. A remarkable decrease in the wear rate and volume values is obtained for the sample sintered at 1250 °C (32.1610–3 μm3 (N.m)− 1) compared to other samples sintered at 1150 and 1250 °C. Under wet tribological conditions, the abrasive and adhesive wear mechanisms were identified as the main degradation mechanisms for all sintered samples.

Self-Annealing Phenomena in the Cold-Rolled and Cryo-Rolled Copper Alloys: A Review

Severely deformed copper (Cu) alloys showed the self-annealing behaviour when exposed at room temperature (RT) for a prolonged time. This phenomenon results in the evolution of self-annealed grains, dislocations annihilations, and a decrease in the strength. The present review work addresses the evolution of self-annealed microstructures in room-temperature-rolled (RTR) and cryogenic-rolled (CR) Cu alloys, including various grades of Cu alloys such as ETP Cu, Cu-Fe-P, Cu-Sn-Mg alloys that were studied in terms of RT softening. Static recrystallization (SRX) at room temperature (RT) was observed in the highly deformed RTR and CR Cu alloy samples. Both discontinuous SRX (DSRX) and continuous SRX (CSRX) were responsible for the nucleation of small grains at RT. Particle-stimulated nucleation (PSN) also contributed to small-grain formations around Cu2O particles in ETP Cu. However, no PSN was reported for the Cu-Fe-P and Cu-Sn-Mg alloys. The formation of strain localizations (SLs) and shear bands (SBs) was observed in the deformed Cu alloys; these sites were preferred for grain nucleation during RT recrystallization.

Experimental investigation on selective laser melting additive manufacturing of non-ferromagnetic heterogeneous material based on TiNi alloy with Ta coating

In order to manufacture non-ferromagnetic heterogeneous material by Selective Laser Melting (SLM), it is necessary to solve the separation problem of non-ferromagnetic mixed powders after SLM forming. This research presents how to resolve this problem using TiNi/Ta mixed powders by ultrasonic vibration screening method and the analysis of SLM manufacturing experiment for non-ferromagnetic heterogeneous material. The purity of TiNi and Ta powders after separation could reach 99.7087%wt% and 98.8501wt% respectively, which both reached a relatively high purity. A TiNi alloy sample with Ta coating and TiNi/Ta gradient transition was manufactured successfully by SLM. The material interface of the sample achieves metallurgical bonding, and the color of the sample profile shows a gradient transition. The EDS analysis shows that the material composition changes from Ta -&gt;Ta/TiNi gradient -&gt;TiNi from surface to inside of the sample. The Ta coating contains over 92.5wt% Ta, and the TiNi matrix contains over 98.69wt% TiNi. Along the powder laying direction, it is difficult to clean the small powder near the solid-powder or solid-solid interfaces made of two different materials, which causes micro polluted areas near the interfaces. This study also provides a new method for integrated manufacturing of TiNi alloy part with Ta coating.

Study on the deformation behavior of AZ31B-O magnesium alloy with the VPSC model

The mechanical anisotropy of the magnesium alloy AZ31B-O was investigated using the Viscoplastic-Self-Consistent (VPSC)-Twinning and Detwinning (TDT) model. The anisotropic behavior of the material under uniaxial strain was studied using five distinct sheet orientations. In order to investigate the mechanical behavior under uniaxial compression, four alternative specimen orientations were employed. The VPSC model with the TDT mechanism was used to simulate the uniaxial tension and compression experiments. For tensile strain, the magnesium alloy samples were mainly regulated by base slip and prismatic slip. In compression of magnesium alloy samples, it was dominated by basal slip and {10–12} twinning. In all compression specimens, the grain c-axes are parallel to the compression axis regardless of the initial orientation. The r-values under different uniaxial strain paths have been also predicted by using the VPSC-TDT model. The negative r-values under uniaxial compression along RD to TD were further explained. The contribution of {10–12} twinning to plastic strain and the extra hardening induced by {10–12} extension twinning were discussed in depth. This study confirms that the extra hardening induced by {10–12} extension twinning will perform an important function when the twin volume fraction reaches a degree of about 50% with the active pyramidal slip at the same time.

Tolerance of several construction materials and polycrystalline SiC to blistering and flecking due to ion implantation and annealing

The results on the tolerance of several construction materials (D16T alloy, Zr, ЭИ-847, 12Х18Н9Т steels) and polycrystаlline SiC to blistering and flecking after irradiation with 500 keV He+ ions and following annealing have been high-lighted. Samples of stainless steels, zirconium, D16T alloy and silicon carbide were irradiated with helium ions in the range from 1016 to 3 · 1018 ion/cm2. Immediately after irradiation and annealing under temperatures from 300 to 750 °C, the optical microscopy was used to study the structure of surface layers. Temperature and fluence ranges of tolerance to blistering and flecking were determined for all examined materials. Primary types of material structure distortions were reviewed.

Effect of Controlled Heat Treatment and Aluminum Additions on the Strengthening of Cu–Ni-Based Alloys

In this investigation, Cu–Ni alloys with different aluminum additions were synthetized under a vacuum atmosphere to reduce the material density. Annealed alloys in a He atmosphere with low aluminum concentration exhibited a coarse dendritic structure, while samples with high aluminum concentration exhibited a refined dendritic structure. Structural defects analyses have shown relatively low vacancy concentrations. Hardness evaluations indicated an increment by approximately 5 times i.e., 370 HVN, more than that for the alloyed samples compared with the as-cast and unalloyed samples. Compression tests have shown a noticeable strengthening improvement (360 MPa), mainly in samples heat treated with 10 at.% Al, while samples with 5 at.% Al showed an acceptable resistance (270 MPa) as well. In general, the sample with 10 at.% Al presented the best performance to be considered as potential structural material.