Presence Of Intermetallic Phases Research Articles

Effect of titanium on the structural, mechanical and surface properties of CoCrFeMnNiTix high entropy alloy fabricated by selective laser melting

In this study, the effect of titanium (Ti) on the microstructure, mechanical properties, wear resistance and corrosion behavior of CoCrFeMnNi high-entropy alloy (HEA) was examined. The selective laser melting (SLM) method was used to produce HEAs without Ti addition (HEA-1) and with Ti additions of 3 and 5 wt% (HEA-2 and HEA-3, respectively). While the HEA-1 sample exhibited a single-phase face-centered cubic (FCC) structure, the HEA-2 and HEA-3 samples exhibited intermetallic phase structures (Sigma and Laves) along with FCC. The addition of Ti and the presence of intermetallic phases in the HEA-2 sample revealed an improvement in mechanical properties without reducing the ductility value of the structure. However, in parallel with the increasing Ti ratio, the formation of more brittle intermetallic phases in the microstructure of the HEA-3 alloy caused a significant increase in strength but a decrease in ductility. Microstructural examinations revealed that all alloys had a cellular/dendritic structure and the relative densities of the samples were above 99%. While the ultimate tensile stress (UTS) of the HEA-1 sample was 548 MPa and the UTS of the HEA-3 alloy was 832.1 MPa, elongation values were obtained as 48% and 2%, respectively. HEA-2 sample exhibited more ideal results with an elongation value of approximately 22% and UTS values of 760.8 MPa. It was observed that the addition of Ti significantly increased the wear resistance in sliding conditions due to the increase in the hardness of the alloy. The highest hardness and lowest wear rate were obtained with HEA-3 coded samples. The HEA-1 sample exhibited the best corrosion rate, with higher corrosion potential (Ecorr) and lower corrosion current density (Icorr) values. The highest corrosion rate was observed in the HEA-3 sample.

Dry Sliding Wear and High-Velocity Impact Behaviour of Spark Plasma Sintered Ti-Ni Binary Alloys

This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni binary alloys produced at varying nickel content with alloy steel ball as the counterface material, at room temperature under varied applied normal loads. Finite element modeling was used to investigate the high-velocity impact response of the sintered alloys due to the dimensional constraint associated with SPSed samples. Microstructural analysis results revealed the presence of intermetallic phases of Ti-Ni with increasing nickel content. The best wear resistance ranging from 0.25 x 10-3 mm3/Nm to 0.22 x 10-3 mm3/Nm across all applied loads was obtained in Ti-6Ni alloy. This was attributed to the compaction of the protective triboxide and carbide layers on the surface of the sample. Oxidative and wear by adhesion were observed at low applied normal load while at high loads the prevalent wear mechanism was abrasive with reduced influence of oxidative and adhesive wear. Finite element analysis results also showed that Ti-6Ni alloy possessed the optimum combination of absorbed energy and ductility to reduce the possibility of brittle failure under impact loading. Keywords: Ti-Ni binary alloys; Spark plasma sintering; Dry sliding wear; High-velocity impact; Finite element analysis.

The Use of Ion Milling for Surface Preparation for EBSD Analysis.

An electron backscattered diffraction (EBSD) method provides information about the crystallographic structure of materials. However, a surface subjected to analysis needs to be well-prepared. This usually requires following a time-consuming procedure of mechanical polishing. The alternative methods of surface preparation for EBSD are performed via electropolishing or focus ion beam (FIB). In the present study, plasma etching using a glow discharge optical emission spectrometer (GD-OES) was applied for surface preparation for EBSD analysis. The obtained results revealed that plasma etching through GD-OES can be successfully used for surface preparation for EBSD analysis. However, it was also found that the plasma etching is sensitive for the alloy microstructure, i.e., the presence of intermetallic phases and precipitates such as carbides possess a different sputtering rate, resulting in non-uniform plasma etching. Preparation of the cross-section of oxidized CM247 revealed a similar problem with non-uniformity of plasma etching. The carbides and oxide scale possess a lower sputtering rate than the metallic matrix, which caused formation of relief. Based on obtained results, possible resolutions to suppress the effect of different sputtering rates are proposed.

Effect of boron carbide and Kaoline reinforcements on the microstructural and mechanical characteristics of aluminium hybrid metal matrix composite fabricated through powder metallurgy technique

ABSTRACT In the present work Al- 10% B4C- X% Kaoline (X = 0, 2, 4, 6, 8) hybrid metal matrix composite (HMMC) was fabricated through powder metallurgy technique. Physical and mechanical properties like density, Hardness, Porosity, Ultimate tensile strength (U.T.S) and Impact energy were studied for the fabricated composite samples. Results concluded that there was a 91.93% increment in hardness and 75% increment in U.T.S of the fabricated samples was observed for Al-10%B4C-4%Kaoline HMMC. However, incorporation of kaoline reinforcement beyond 4% leads to the formation of agglomerates in the composites reducing the U.T.S from 238 MPa to 186 MPa and hardness from 119 VHN to 101 VHN. The fabricated composite specimens were characterised using an X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The XRD patterns reveal the presence of Aluminium, B4C and kaoline particles. In addition to this, the presence of intermetallic phases was observed for Al-10%B4C-6% Kaoline and Al-10%B4C-8% kaoline HMMC. Uniform distribution of reinforcements and formation of agglomerations for 6% and 8% kaoline reinforcements was confirmed by SEM and their respective EDS mapping. Results showed that the Al-10 % B4C- 4% Kaoline has superior mechanical properties compared to monolithic aluminium

CHARACTERIZATION OF CHROMIUM NITRIDE PRECIPITATION IN THE HEAT AFFECTED ZONE OF THE SUPERDUPLEX STAINLESS STEEL UNS S32750: AN EXPERIMENTAL AND NUMERICAL ANALYSIS

It is well known that pitting corrosion resistance of duplex and superduplex stainless steels strongly depends on 
 microstructural characteristics such as ferrite/austenite proportion, presence of intermetallic phases and elemental partitioning between the austenite and ferrite phases. In particular, during the welding operation, very fine chromium nitrides may precipitate 
 within ferrite grains of the heat affected zone drastically reducing the corrosion resistance of welded joints of duplex and super duplex stainless steels. However, due to their small size and low distribution, analyzing the chemical composition and crystallography of chromium nitrides is quite difficult and only a restricted number of advanced techniques of investigation may discriminate their signal from the surrounding matrix. This work is aimed at supporting the microstructural characterization of a welded joint of a superduplex stainless steel by means of a field-emission gun scanning electron microscope. Sub-micron chromium nitride precipitates, identified within the ferritic grains of the heat affected zone, are recognized to be the main reason for the reduced pitting corrosion resistance of the analyzed welded joints. The results are supported by a multi-pass welding process numerical simulation aimed at estimating the cooling rates promoting chromium nitride precipitation in the heat affected zone.

Structure and corrosion resistance of Al–Cu–Fe alloys

The microstructure and electrochemical properties of Al–Cu–Fe alloys with the atomic compositions of Al65Cu20Fe15, Al78Cu7Fe15 and Al80Cu5Fe14Si1 have been studied. The alloys were produced by induction melting of pure elements with copper mold casting. The microstructure of the alloys was analyzed by X-ray diffraction and high-resolution transmission electron microscopy. The formation of quasicrystalline phases in the Al–Cu–Fe alloys was confirmed. The presence of intermetallic phases was observed in the alloys after crystallization in a form of ingots and plates. The electrochemical measurements were conducted in 3.5% NaCl solution. The electronic structure of the alloys was determined by X-ray photoelectron spectroscopy. The post corrosion surface of the samples was checked using a scanning electron microscope equipped with the energy-dispersive X-ray detector. It was observed that the Al65Cu20Fe15 alloy had the highest corrosion resistance. The improved corrosion resistance parameters were noted for the plate samples rather than those in the as-cast state. And the hardness of the Al65Cu20Fe15 alloy was significantly higher than the other alloy samples.

Al-Si-Zn Behaviouron Interface of AR500 Steel and AA7075 Aluminium Alloy BrazedJoint

The brazing of steel and aluminium alloy using low melting point aluminium based fillers has been extensively studied and the technique has been used in many industries, especially the automotive industry. The strength and failure mode of AR500 steel and AA7075 aluminium alloy brazing joint using the Al-Si-Zn filler metal will be measured and calculated in this paper. However, the adverse effect of intermetallic phases formation on the joint strength has limited the application of this joining method.These dissimilar metals possessing a high strength joint would be of benefit to industry especially in reducing the weight of products. The torch brazing method using Al-Si-Zn base filler metal wasused to join AR500 steel and AA7075 aluminium alloy in this study. The intermetallic phase formation of the brazing on was investigated by scanning electron microscopy and the mechanical strength of the joints was evaluated by shear testing, flexural testing and low velocity impact testing. A maximum shear load of 6460 N was obtained. The presence of intermetallic phases was found to have some effect on the strength of the brazed joint. However, overall, this brazing process using Al-Si-Zn filler metal facilitates the joining of these dissimilar metals to improve the mechanical properties of the joint

Investigation of surface roughness effects on microstructural and mechanical properties of diffusion bonding between dissimilar AZ91-D magnesium and AA6061 aluminum alloys

The effects of surface roughness were studied on microstructural and mechanical properties of solid-state diffusion bonding between two dissimilar alloys of magnesium AZ91-D and aluminum 6061 by means of hot pressing. Although applied pressure, temperature, and duration of diffusion bonding are known as the most effective parameters, surface roughness can alter the mechanical and microstructural properties remarkably, which is usually neglected. To investigate the effect of surface roughness between 0.06 and 0.15 μm, the width of the diffusion bond in the interfacial transition zone (ITZ) and the presence of intermetallic phases were analyzed. Moreover, microhardness, shear strength, and fracture surfaces were evaluated. The results exhibit that in the applied roughness range, the bond width and the microhardness of the joints improved by increasing the surface roughness of the both metals; however, the shear strength decreased. It may be attributed to more disruption of the oxide films on the metal surfaces in the rougher samples and also increase in the effective interface boundary during the process. Consequently, there would be more chance for aluminum-magnesium contacts, resulting in more diffusion, further formation of brittle intermetallic phases (such as Al12Mg17 and Al3Mg2), and therefore more hardness and less shear strength.

JOINIG OF MG ALLOY AZ31B BY SELECTED TECHNOLOGIES

This contribution presents metallurgical joining of Mg alloy AZ 31B by several technologies - Friction Stir Welding - FSW, Laser Beam Welding - LBW, soldering and their mutual comparison. The difficulty of joining Mg alloys is connected with the strong MgO layer, low ductility of the weld metal (WM), a presence of intermetallic phases connected with the hardness increase. To successfully join Mg alloys, a precise setting of welding parameters is needed. The welds are susceptible to low mechanical properties as all samples fractured at WM. From the tested methods, laser beam welding proved the best results, because laser welding is the fastest and weld strength reached the highest values, i.e. 87% of BM (base metal) strength.

Impact of tungsten on microstructure, hardness and wear rate of AISI 304 stainless steel surface alloyed under nitrogen environment

An examination was carried out on AISI304 Stainless steel with tungsten by surface modification using Gas Tungsten Arc as a heat source at a constant flow of nitrogen gas added to Argon shielding atmosphere. The microstructure of the W - modified area were observed using a metallurgical microscope. The composition of the surface modified layers were analyzed using EDS. The result of the EDS analysis confirmed the presence of W and N2 content in the modified layers. Further, the presence of intermetallic phases were found during the XRD analysis. Hardness measurements were carried out along the depth direction. The hardness increased by 2010HV on the W- modified layer under N2 atmosphere compared to the 277HV of the substrate. It is noticed that the wear resistance in the surface modified area improved to 0.8 × 10−4 mm3 / N-m from 10.94 × 10−4 mm3 / N-m of the substrate. The reduction in grain size, formation of intermetallic phases, and dispersion of W – particle in the modified layers has improved the hardness and the wear resistance.

Electrochemical Corrosion Behavior of High Velocity Oxy-Fuel (HVOF) Superalloy Coatings On Ductile Irons

In this study, alloyed and unalloyed ductile irons (DI) were coated with two different Ni-based superalloy materials by HVOF method. Microstructure and phase analyzes of the coatings were performed by using SEM, EDX, XRD methods. The electrochemical corrosion behavior of alloyed and unalloyed DI is investigated in 3.5% (w / v) NaCl solution. As a result of the characterization studies, it was observed that a dense non-porous coating layer of about 80 μm thickness was obtained on the cast iron samples and continuous adhesion was provided between the coating and the substrate. It has been determined that the cast iron coated with AMDRY 9624 contains γ and β intermetallic phases and the coating produced with AMDRY 9951 commercial powder contains only γ phase. As a result of coating process, the corrosion rate of the alloyed and unalloyed spherical graphite cast irons is reduced. Also, the corrosion rate of the coating produced with AMDRY 9951 is higher than the coating produced with AMDRY 9624. The presence of intermetallic phases in the coating produced with AMDRY 9624 increased the corrosion resistance of the coatings.

Solidification Behavior of Duplex Stainless Steel (UNS S32205) Welds as a Function of WRC–1992 Diagram Equivalents and Cooling Rate

Duplex stainless steels solidify as 100 % Ferrite, however solidification of Duplex Stainless steel welds is a function of Chromium equivalent and Nickel equivalent alloying elements, filler metal and base metal composition and associated weld thermal cycle. Resultant solidification mode behavior and hence final weld metal microstructure is always a matter of interest among researcher because mechanical properties and corrosion properties are depending on weld metal ferrite content. The present research is to investigate the solidification mode behavior of duplex stainless steel welds with varying Chromium equivalent and Nickel equivalent ratios and associated weld cooling rate. In order to meet this objective, weld coupon were prepared using experimental Low Nickel, Medium Nickel and High Nickel electrodes using SMAW process, step wise increased in Nickel content from commercially available standard 09 weight percentage Nickel in E2209 design. WRC-1992 Diagram has been used to calculate Chromium Equivalent and Nickel equivalent and predict Ferrite Number using compositions of Base metal and Nickel enriched experimental electrodes. Microstructure characterization of all weld coupons is carried out using ASTM A 923 Method. Calculated values were correlated with the different microstructures developed. According to the findings of the studies, weld produced with higher Nickel content electrode, when cooled with maximum rate approximately 100.8 °C/ Sec , considered under study, exhibited FA-mode of solidification with as low as 1.71 Cr eq /Ni eq ratio and there was no noteworthy presence of intermetallic phases and precipitations in as-weld microstructures at approximate retained ferrite level of 15 Ferrite Number.

Obtaining the functional intermetallic Ni–Ti coatings by heterophase transfer combined with laser treatment

The results of the investigation of the intermetallic Ni–Ti system coating obtained by complex method of cold gasodynamic spraying and laser treatment are presented. The dependence of the coating charge composition on the initial powder composition is shown. Its structure, porosity, and microhardness are studied, and also the results of X-ray phase analysis confirming the presence of intermetallic phase are presented. The microhardness increased more than 5 times to 632 HV, and porosity decreased 25 times up to 0.2%. Investigation of the substrate-coating boundary showed the presence of mutual diffusion.

The Effect of Hypervelocity Impact Loading on Explosively Welded Ti/Al/Al Plate

The aim of this paper is to investigate the ballistic properties of explosively welded Ti6Al4V/AA1050/AA2519 laminate under hypervelocity (4000 m/s) impact loading of projectile made of aluminium ball. The paper describes the influence of the projectile impact energy on the structure of the laminate components and delamination of bonds depending on its strength and presence of intermetallic phases. Observation of the failure is performed for the plate impacted for aluminium alloy side. Results revealed ductile shearing as a dominant process leading to perforation.

Mechanical properties and corrosion behaviour of Al-Si alloys for IC engine

The paper describes the mechanical properties and the corrosion behaviour of three Al?Si alloys in 0.5 M NaCl solution. The alloys have exhibited similar values of hardness, but the highest tensile strength and the lowest elongation have shown the specimens of alloy with 11.38 % of silicon. Higher content of both copper and magnesium has contributed to better tensile strength and lower elongation of as-cast hypoeutectic alloys. The harmful effects of iron on mechanical properties of all alloys have been reduced to some extent by nickel and cobalt addition. The differences in the values of the open circuit potential of the examined alloys were insignificant. The thickness of the protective oxide layer has increased over time, and the layer has become very compact. Slight differences in the values of the corrosion potential of the alloys were determined, whereas the lowest value of the corrosion current was indicated for the hypereutectic alloy. The presence of intermetallic phases in the alloys has shown that the oxide film was not consistent. The severe pits have not been found at the surface of the corroded samples. Based on the obtained results, the examined alloys may be used for the manufacturing of the internal combustion engine parts.

Effect of Solution Annealing Time on the Microstructure and Corrosion Resistance of Duplex Stainless Steel

The formation of intermetallic phases during thermal treatments is a decisive point for the performance of duplex stainless steels, which may prevent the obtaining or provoke degradation of their properties. This paper presents an investigation on the corrosion resistance of duplex SAF 2205 steel as received and after solution annealing treatment. The objective was to evaluate the correlation between the solution annealing time, the resulting microstructural changes and the corrosion resistance of the steel through electrochemical tests of cyclic potentiodynamic polarization and double-cycle potentiokinetic reactivation (DL-EPR). The heat treatments were performed at 1100° C for 30, 120 and 240 min with subsequent air cooling. The results of the DL-EPR showed that although there was no presence of intermetallic phases even with the absence of intermetallic phases, the solution annealing time influenced the degree of chromium depletion of the samples, so that with the increase of time, there was an increase in the degree of chrome depletion.

Electrical Conductivity in Electrodeposited Cu-Ge(O) Alloy Films

Integrated circuits currently use mainly copper as the interconnect material; unfortunately the ongoing miniaturization currently requires materials with higher electromigration resistance and possibly improved conductivity. In this context we report on the structure, microstructure and electrical properties of a series of Cu-Ge(O) alloy films, electrodeposited from an alkaline tartrate electrolyte. The composition of the films varies between zero and 20 at% Ge, with a significant incorporation of oxygen. Film morphology is dense and uniform, with Cu-Ge films exhibiting smaller apparent grain size (∼50 nm) with respect to Cu films grown from a similar electrolyte. Solid solutions and phase mixtures of a solid solution with the intermetallic are observed with increasing Ge fraction; the presence of intermetallic phases is confirmed by TEM imaging and diffraction. The resistivity of 50 nm thick films follows the published trend, with a slight increase of the value upon solid solution formation and a minimum in correspondence of the intermetallic composition. Thicker films (∼1 um) on the other hand show a different trend, with resistivity increasing with Ge and O at%; in this case the resistivity is probably dominated by the oxygen incorporation.

Effect of explosive mixture on quality of explosive welds of copper to aluminium

The aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type. Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4 were only identified in welds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint.

Effect of the Fe/Cu Relationship Corrosion and low Alloying Elements on Corrosion Behavior of Cast Aluminum Parts

ABSTRACTThe aim of this study is to compare the corrosion rate of aluminum alloys for ornamental pieces. Three Fe/Cu relationships were tested in order to improve hardness and brightness in aluminum pieces since these alloys are used in the making of ornamental pieces. The variation on Fe/Cu content could result in modification on corrosion rate, since a metallographic characterization must be carried out identifying the presence of intermetallic phases. The presence of these elements could result in increasing corrosion rate, or even in modification of corrosion morphology, so localized corrosion could be expected.The assessment of corrosion rate was carried out in saline media, since chlorides are ions that promote localized corrosion. Electrochemical techniques (polarization curves and Tafel plots) were used in order to evaluate the attack in aluminum pieces; electrochemical impedance spectroscopy was also employed with voltage amplitude of 10 mV rms, and a frequency range from 10,000 Hz to 0.01 Hz. A typical three electrodes cell was used, exposing an area of one cm2. Before polarization, open circuit potential was monitored for an hour looking for a steady state. All conditions were tested for triplicate.The behavior of open circuit potential vs. time, and polarization curves was analyzed; a corrosion mechanism is proposed according to the electrochemical control. Polarization rate was calculated by using Tafel plots and, an electrochemical impedance spectroscopy analysis by using equivalent electric circuits is shown. Electrochemical impedance will yield information about corrosion morphology that is backed with microscopic inspection.The objective of this study is to compare the corrosion rate of aluminum alloys for ornamental pieces in order to determine the effect of the relationship Fe/Cu on the corrosion mechanism in aluminum parts for ornamental pieces.

Structure and properties of modified compocast microsilica reinforced aluminum matrix composite

Abstract A356 aluminum alloy reinforced with 7 wt.% microsilica composites was produced by the three different processing routes viz. liquid metal stir casting followed by gravity casting, compocasting followed by squeeze casting and modified compocasting route and their properties were examined. Microstructure of liquid metal stir cast Al MMC shows agglomeration of particles leading to high porosity level in the developed material. Adopting new route of compocasting followed by squeeze casting process prevents the agglomeration sites with uniform distribution and dispersion of the dispersoids in the matrix metal. Modified compocasting process reduces the segregation of particles in the final composites thus enhancing the mechanical, tribological and corrosion properties of the composites. Superior wear-resistance properties were exhibited by the modified compocast composite compared to the unreinforced squeeze cast alloy and abrasive type wear mechanism was observed in the case of composite. Increasing the sliding speed resulted in the quick evolution of tribolayer and the wear rate of composite gets reduced. The presence of intermetallic phases like MgAl 2 O 4 , NaAlSi 3 O 8 and KAlSi 3 O 8 has a favorable effect on increased corrosion resistance of the composite. Microsilica particles significantly enhanced the compressive strength of modified compocast composites compared to the unreinforced squeeze cast Al alloy.