Microstructure and wear properties of laser clad Fe−Cr−Mn−C alloys

The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10∶1∶1 were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO₂ laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved wear resistance is attributed to the fine distribution of metastable M₆C carbides.     

Processing,microstructure, and properties of laser-clad Ni alloy FP-5 on Al alloy AA333

This article describes the results of laser cladding Ni alloy FP-5 on Al alloy AA333, microstructure and crystal structure characterization, and properties of the clad evaluated by Vickers hardness measurement and wear testing. Direct cladding of Ni alloy on Al alloy creates brittle Ni _x Al _y compounds in the interface, which make the interface very brittle, and result in cracking at the interface. The compound formation is avoided by introducing an intermediate layer of Cu or bronze. The cracking tendency of the clad is prevented by preheating the substrate to 673 K. The microstructure and crystal structure of the clad and interface are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Five phases in the clad layer (including three new phases) and two phases in the interface are identified by convergent beam electron diffraction (CBED) and selected area diffraction (SAD) studies. The mechanical properties of the laser-clad Ni alloy are evaluated by Vickers hardness measurements and wear testing, which show superior results over Cu- and Fe-based alloys.     

Microstructure of laser clad Ni- Cr- Al- Hf alloy on a γ′ strengthened ni- base superalloy

Alloys and coatings for alloys for improved high temperature service life under aggressive atmo-spheres are of great contemporary interest. There is a general consensus that the addition of rare earths such as Hf will provide many beneficial effects for such alloys. The laser cladding technique was used to produce Ni-Cr-AI-Hf alloys with extended solid solution of Hf. A 10 kW CO₂ laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron (STEM) microscopy were employed to characterize the microstructure of alloys produced during laser cladding processes. Microstructural studies revealed grain refinement, considerable in-crease in solubility of Hf in the matrix, Hf-rich precipitates, and new metastable phases. The size and morphology of γ′ (Ni₃Al) phase were discussed in relation to its microchemistry and the laser processing conditions. This paper will report the microstructural development in this laser clad Ni-Cr-AI-Hf alloy. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign.     

Effect of Gd on microstructure,mechanical properties and wear behavior of as-cast Mg–5Sn alloy

Effect of minor Gd addition on the microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn-based alloy was investigated by means of OM, XRD, SEM, EDS, a super depth-of-field 3D system, standard high-temperature tensile testing and dry sliding wear testing. Minor Gd addition has strong effect on changing the morphology of the Mg–5Sn binary alloy. Gd addition benefits the grain refinement of the primary α-Mg phase, as well as the formation and homogeneous distribution of the secondary Mg₂Sn phase. The mechanical properties of the Mg–5Sn alloys at ambient and elevated temperatures are significantly enhanced by Gd addition. The wear behavior of the Mg–5Sn alloy is also improved with minor Gd addition. The alloy with 0.8% Gd addition exhibits the best ultimate tensile strength and elongation as well as the optimal wear behavior. Additionally, the worn surface of the Mg–5Sn–Gd becomes smoother in higher Gd-containing alloys. The best wear behavior of alloy was exhibited when Gd addition was up to 0.8%, showing a much smoother worn surface than that of control sample. The improvement of tensile properties is mainly attributed to the refinement of microstructure and the increasing amount and uniform distribution of Mg₂Sn phase. The larger amount of Mg₂Sn phase uniformly distributed at the grain boundary of Mg–Sn–Gd alloys act as a lubrication during sliding, and combined with smaller grain size improve wear behavior of the binary alloy.     

Effect of extended solid solution of Hf on the microstructure of the laser clad Ni-Fe-Cr-Al-Hf alloys

Alloys and coatings for alloys for improved high temperature service life under aggressive atmosphere are of great contemporary interest. There is a general consensus that addition of reactive elements such as Hf will provide many beneficial effects for such alloys. The laser cladding technique was used to produce Ni-Fe-Cr-Al-Hf alloys with extended solid solution of Hf. A 10 kW CO₂ laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron (STEM) microscopy were employed for microstructural evolution of alloys produced during laser cladding processes. The electron probe microanalysis and the auger electron spectroscopy were also used for micro-chemical analysis of different phases. Microstructural studies revealed a high degree of grain refinement, considerable increase in solubility of Hf in matrix and Hf rich precipitates and new metastable phases. This paper will report the microstructural development in this laser clad Ni-Fe-Cr-Al-Hf alloy.     

Some observations of the influence of δ-ferrite content on the hardness,galling resistance,and fracture toughness of selected commercially available iron-based hardfacing alloys

Iron-based weld hardfacing deposits are used to provide a wear-resistant surface for a structural base material. Iron-based hardfacing alloys that are resistant to corrosion in oxygenated aqueous environments contain high levels of chromium and carbon, which results in a dendritic microstructure with a high volume fraction of interdendrite carbides which provide the needed wear resistance. The ferrite content of the dendrites depends on the nickel content and base composition of the iron-based hardfacing alloy. The amount of ferrite in the dendrites is shown to have a significant influence on the hardness and galling wear resistance, as determined using ASTM G98 methods. Fracture-toughness (K _IC) testing in accordance with ASTM E399 methods was used to quantify the damage tolerance of various iron-based hardfacing alloys. Fractographic and microstructure examinations were used to determine the influence of microstructure on the wear resistance and fracture toughness of the iron-based hardfacing alloys. A crack-bridging toughening model was shown to describe the influence of ferrite content on the fracture toughness. A higher ferrite content in the dendrites of an iron-based hardfacing alloy reduces the tendency for plastic stretching and necking of the dendrites, which results in improved wear resistance, high hardness, and lower fracture-toughness values. A NOREM 02 hardfacing alloy has the most-optimum ferrite content, which results in the most-desired balance of galling resistance and high K _IC values.     

Mechanical properties and fracture behavior of an ultrafine-grained Al-20 wt pct Si alloy

The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder size <26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (<26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pct Fe (powder size: 60 to 120 μm) alloys. With decreasing powder size from 45 to 106 μm to <26 μm, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worn surface in comparison to the bars from the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders.     

The Microstructure and tensile properties of a splat-quenched Al-Cu-Li-Mg-Zr alloy

The microstructure and tensile behavior of an Al-3Cu-l.6Li-0.8Mg-0.2Zr alloy, produced by splatquenched powder metallurgy processing, were studied. The alloy exhibited homogeneous deformation, both in bulk samples and duringin situ TEM studies. This is in contrast to the strain localization that is frequently observed in Mg-free Al-Cu-Li-X alloys. The difference in deformation mode is attributed to a fine distribution of Ś (Al₂CuMg) which precipitates up to the grain boundaries. A processing treatment involving 2 pct stretch prior to aging resulted in a yield strength of 555 MPa, a reduction in area of 29 pct, and a strain to fracture of 8.8 pct. This represents an attractive improvement in specific properties compared with 7075-T76 having a similar texture.     

Experimental Investigation of Magnesium-Base Nanocomposite Produced by Friction Stir Processing: Effects of Particle Types and Number of Friction Stir Processing Passes

In this research, nanosized SiC and Al₂O₃ particles were added to as-cast AZ91 magnesium alloy, and surface nanocomposite layers with ultrafine-grained structure were produced via friction stir processing (FSP). Effects of reinforcing particle types and FSP pass number on the powder distribution pattern, microstructure, microhardness, and on tensile and wear properties of the developed surfaces were investigated. Results show that the created nanocomposite layer by SiC particles exhibits a microstructure with smaller grains and higher hardness, strength, and elongation compared to the layer by Al₂O₃ particles. SiC particles do not stick together and are distributed separately in the AZ91 matrix; however, distribution of SiC particles is not uniform in all parts of the stirred zone (SZ), which causes heterogeneity in microstructure, hardness, and wear mechanism of the layer. Al₂O₃ particles are agglomerated in the different points of matrix and create alumina clusters. However, distribution of Al₂O₃ clusters in all parts of the SZ is uniform and results in a uniform microstructure. In the specimen produced by one-pass FSP and SiC particles, the wear mechanism changes in different zones of SZ due to the nonuniform distribution of particles. However, in the specimen produced by Al₂O₃ particles, the wear mechanism in all parts of the SZ is the same and, in addition to the abrasive wear, delamination also occurs. Increasing FSP pass number results in improved distribution of particles, finer grains, and higher hardness, strength, elongation, and wear resistance.     

Developing a M6C-Reinforced High-Cr White Iron for Abrasive Wear Application

Fast removal of soft phases (e.g., pearlite and ferrite) in the iron matrix limits the wear life of high-Cr white irons. To address this shortcoming, the authors successfully produced fine networks of M₆C carbide in a high-Cr white iron through extensive thermodynamic calculations. Fishbone-like networks of M₆C carbides were observed with an optical microscope. It was experimentally determined that such carbide networks protected the soft matrix and increased the overall hardness. Additionally, electron backscattered diffraction was conducted, which showed that the alloy contained phases of M₇C₃, M₆C, ferrite, and retained austenite. Solidification sequence was determined by correlating the thermodynamic equilibrium calculation results with the size and distribution of each phase. A dry sand/rubber wheel apparatus following ASTM standard G65 Procedure A was utilized to assess the abrasive wear performance of the developed alloy. Results showed that the volume loss of the developed material was 25 pct less than that of conventional high-Cr white irons. Wear scars were investigated using a scanning electron microscope, and the improved wear resistance was attributed to the “buffer” effect and plastic deformation of the introduced M₆C carbide networks.

     

Effect of B on the microstructure and mechanical properties of mechanically milled TiAl alloys

The present study is concerned with γ-(Ti₅₂Al₄₈)_100−x B _x (x=0, 0.5, 2, 5) alloys produced by mechanical milling/vacuum hot pressing (VHPing) using melt-extracted powders. Microstructure of the as-vacuum hot pressed (VHPed) alloys exhibits a duplex equiaxed microstructure of α₂ and γ with a mean grain size of 200 nm. Besides α₂ and γ phases, binary and 0.5 pct B alloys contain Ti₂AlN and Al₂O₃ phases located along the grain boundaries and show appreciable coarsening in grain and dispersoid sizes during annealing treatment at 1300 °C for 5 hours. On the other hand, 2 pct B and 5 pct B alloys contain fine boride particles within the γ grains and show minimal coarsening during annealing. Room-temperature compressing tests of the as-VHPed alloys show low ductility, but very high yield strength >2100 MPa. After annealing treatment, mechanically milled alloys show much higher yield strength than conventional powder metallurgy and ingot metallurgy processed alloys, with equivalent ductility to ingot metallurgy processed alloys. The 5 pct B alloy with the smallest grain size shows higher yield strength than binary alloy up to the test temperature of 700 °C. At 850 °C, 5 pct B alloy shows much lower strength than the binary alloy, indicating that the deformation of fine 5 pct B alloy is dominated by the grain boundary sliding mechanism. This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees.     

Study of dilution in laser cladding of a carbon steel substrate with Co alloy powders

High power diode laser with coaxial powder injection was used to deposit single tracks of cobalt alloy on to a carbon steel plate in order to study dilution. Two different methods to evaluate dilution are proposed and validated: dilution results to be proportional to the average percent or iron present in the clad. To study the correlations between dilution and processing parameters, clads were produced in different processing conditions. Dilution is correlated with the specific energy, and equation to estimate the average iron contamination of the clads was found. ‘Trial and error’ method was applied to improve this estimation. A statistically better prediction of the iron contamination is obtained when the combined parameter P^2.5/F⁴ is used. Dilution influences clad microstructure and thus hardness of the final coating, which decreases on increasing dilution. Phase distribution is also affected by dilution, Fe and C contamination stabilises α-fcc phase.     

Effect of Tin on the Wear Properties of Spray Formed Al–17Si Alloy

In the present study, the effect of Sn on the dry sliding wear behavior of spray formed and hot pressed Al–17Si alloy as a function of applied load and sliding speed has been investigated and compared with that of as-cast alloy. The microstructure of spray formed Al–17Si alloy consists of fine and uniformly distributed Si particles and that of Al–17Si–10Sn alloy consists of fine and uniform dispersion of Si particles and ultra-fine Sn particles in α-Al matrix. Coarse and segregated microstructures were observed in as-cast alloys. The wear resistance of spray formed alloys is higher than that of as-cast alloys. The wear resistance of as-cast Al–17Si–10Sn alloy is higher than that of as-cast Al–17Si alloy. The high wear resistance of spray formed Al–17Si–10Sn alloy is discussed in the light of its microstructural features and the nature of worn-out surfaces.     

Processing and microstructural characterization of Al-Cu alloys produced from rapidly solidified powders

This paper concerns the processing of Al-Cu alloys via a novel powder-metallurgy route. The specific technique used for powder processing involves the rapid solidification of coarse, molten droplets following impulse atomization. This produces a fine, homogeneous, dendritic microstructure within the alloy granules. Following consolidation via hot pressing, the microstructure consists mostly of an Al matrix with fine CuAl₂ particles and partially recrystallized dendrites. Further heat treatment and/or thermomechanical processing completes the spheroidization process in the CuAl₂ phase. Blending powders with different Cu has been used to make materials with a bimodal distribution of the local particle-volume-fraction content. The high temperature (773 K) strength of these materials decreases with increasing CuAl₂ content. This can be explained using a flow model based on superplastic deformation, controlled by diffusion-accommodated sliding at Al grain boundaries. This mechanism may also explain the deformation-enhanced particle coarsening observed during channel-die forging operations.     

Effect of vanadium addition on the microstructure, hardness, and wear resistance of Al0.5CoCrCuFeNi high-entropy alloy

The authors studied the effect of vanadium addition on the microstructure and properties of Al_0.5CoCrCuFeNi high-entropy alloy. The microstructure of Al_0.5CoCrCuFeNiV _x (x=0 to 2.0 in molar ratio) alloys was investigated by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. With little vanadium addition, the alloys are composed of a simple fcc solid-solution structure. As the vanadium content reaches 0.4, a BCC structure appears with spinodal decomposition and envelops the FCC dendrites. From x=0.4 to 1.0, the volume fraction of bcc structure phase increases with the vanadium content increase. When x=1.0, fcc dendrites become completely replaced by bcc dendrites. Needle-like σ-phase forms in bcc spinodal structure and increases from x=0.6 to 1.0 but disappears from x=1.2 to 2.0. The hardness and wear resistance of the alloys were measured and explained with the evolution of the microstructure. The hardness values of the alloys increase when the vanadium content increases from 0.4 to 1.0 and peak (640 HV) at a vanadium content of 1.0. The wear resistance increases by around 20 pct as the content of vanadium increases from x=0.6 to 1.2 and levels off beyond x=1.2. The optimal vanadium addition is between x=1.0 and 1.2. Compared with the previous investigation of Al_0.5CoCrCuFeNi alloy, the vanadium addition to the alloy promotes the alloy properties.     

Improvement in toughness of Fe-Cr-Mn-C steels by thermal-mechanical treatments

High-Cr (about 10 wt pct) Fe-Cr-Mn-C microcomposite lath martensite-austenite structural steels have been developed in order to achieve high strength and high toughness for applications in corrosive environments. Processing by controlled hot rolling and air cooling produces a finegrained alloy with excellent toughness. The alloys are air hardenable, and the microstructure consists of lath martensite packets with retained austenite around the laths. The laths contain fine intralath autotempered carbides. The mechanical properties of the steel so produced are found to be superior to those treated by conventional methods of single or cyclic austenitization treatment. Optical metallography, transmission electron microscopy and scanning electron microscopy (SEM) have been used to characterize the effect of various process variables on the mechanical properties. R. RAMESH and N.J. KIM, formerly with the Department of Materials Science and Mineral Engineering, University of California at Berkeley     

Influence of Air Cooling and Aging on Microstructure and Wear Properties of 3D-Printed and Conventionally Produced Medical-Grade Ti6Al4V ELI Alloy

The emergence of additive manufacturing (AM) in recent years has become one of the most demanded manufacturing technologies in the biomedical and aerospace industries due to its ease of fabrication of components with complex geometry. Ti6Al4V parts manufactured by AM process however require a post-processing to optimize their mechanical properties for engineering applications. The cooling rates after the heat treatment play a significant role in tailoring the final microstructure and properties of medical-grade Ti6Al4V ELI alloys. This study therefore aims to investigate the changes in microstructure and consequently mechanical and wear properties of both AM-fabricated (3D-printed) and conventionally produced Ti6Al4V ELI alloy by the effect of post-heat treatment, air-cooling and aging (200 °C, 500 °C and 800 °C) processes. Typically, the formation of lath colonies and precipitated needle-like lath structures after solutionization (@ 1080 °C) and air cooling above the β-transus yielded a retained cubic β-phase regardless of the manufacturing process. Different spatial distributions of the alpha (α) lath and basket-weave structures as well as coarsened AlTi₃ intermetallic (V-shaped) structures evolve, which later reduced in area fraction in 3D printing. Also, increasing the aging temperatures after slow (air) cooling gradually enhances α-β-phase transformation rates regardless of the manufacturing process because of diffusional redistribution of alloying elements. In addition, the evolution of V-shaped structures improves the hardness (up to 29 pct) and wear performance of 3D-printed materials (up to 126 pct) relative to the conventionally produced materials, regardless of the β content.

     

Microstructural characterization

Rapidly solidified microstructures of Fe-Cr-W-C quaternary alloy deposited on low-carbon steel by laser cladding were investigated. The clad-coating alloy, a powder mixture of Fe, Cr, W, and C with a weight ratio of 10:5:1:1, was processed with a high-power continuous wave CO₂ laser. The developed clad coatings possessed fine microstructures, uniform distributions of al- loying elements, and high microhardness. Analytical electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the crystal structures and microchemistries of the various phases in the clad coatings. The laser processed microstructure comprised fine primary dendrites of a face-centered cubic (fcc) austenitic y phase and interdendritic eutectic consisting of a network of pseudohexagonal M₇C₃ carbides rich in Cr in an fcc austenitic γ phase. The interlamellar spacing in the eutectic matrix was about 20 nm. The relatively high microhardness, about 900 kg_f/mm², of such fine microstructures is attributed to the formation of complex ter- nary carbides uniformly distributed in the eutectic matrix. In situ transmission electron micros- copy (TEM) of thermally treated clad coatings revealed that transformation of the primary γ phase to body-centered cubic (bcc) ferrite (α phase) commenced after heating at 843 K for about 7 minutes. The transformation initiated at the interface of the primary dendrites and the eutectic and propagated gradually into the primary phase. Phase change of the interdendritic γ austenite to a bcc α ferrite occurred after about 30 minutes of hold period at 843 K. Transformation of the M₇C₃ carbides did not occur even after heating at 843 K for about 3.2 hours. The growth of a thin M₂O₃ (M = Fe, Cr) oxide scale was detected after heating at 843 K for approximately 24 minutes. After cooling gradually to room temperature, the softened (723 kgy/mm²) micro- structure consisted of primary dendrites with a bcc α ferrite crystal structure and interdendritic ternary eutectic of untransformed M₇C₃ carbides in α ferrite.     

Microstructure and Properties of Fe–Cr–B–Al Alloy After Heat Treatment

By means of optical microscope, scanning electron microscope, X-ray diffraction, energy dispersive spectrometer, Rockwell and Vickers hardness tester, and wear tester, the microstructure and properties of Fe–10Cr–1B–4Al alloy quenched in different temperature has been studied. The results show that the microstructure of as-cast Fe–10Cr–1B–4Al are composed of pearlite, ferrite and the eutectic borocarbide which shows a network distribution along grain boundaries. The eutectic borocarbides are composed of M₇(C, B)₃, M₂(B, C) and M₂₃(C, B)₆. As the quenching temperature increases, the network structure of eutectic borocarbide breaks, but the type of eutectic borocarbide has no obvious change, and the matrix structure changes gradually from ferrite to pearlite. As the quenching temperature increases, the macro-hardness and the matrix micro-hardness of Fe–10Cr–1B–4Al alloy increases gradually. The macro-hardness and matrix micro-hardness of alloy reach the highest value of 45.7 HRC and 388.1 HV, respectively when the quenching temperature is 1150 °C. The hardness of alloy decreases slightly when the quenching temperature is too high. While quenching at 1150 °C, the alloy has the highest wear resistance and good comprehensive properties.