WCp/Fe metal matrix composites produced by laser melt injection

Laser melt injection (LMI) was used to produce WC particles (WC_p) reinforced metal matrix composites (MMCs) layer on the mild steel. During the LMI process, different parameters were applied, and the processing window of this technique was obtained. The MMCs layers were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM result reveals that none macro-defects except few pores can be found in the MMCs layer, and the WC_p distribute uniformly in the layer. In addition, some new phases can be found in the MMCs layer, where Fe₃W₃C is the predominant phase. At the same time, the amount of dissolved WC_p plays a key role in the microstructure of the MMCs layer. The WC particle dissolved into the melt pool leads to the appearance of reaction products in the matrix, such as various primary Fe₃W₃C dendrites, and the liquid WC remained on the solid WC particle results in the formation of a thicker reaction layer.     

Microstructure of reaction zone in WCp/duplex stainless steels matrix composites processing by laser melt injection

The laser melt injection (LMI) process has been used to create a metal matrix composite consisting of 80μm sized multi-grain WC particles embedded in three cast duplex stainless steels. The microstruture was investigated by scanning electron microscopy with integrated EDS and electron back-scatter diffraction/orientation imaging microscopy. In particular the search of the processing parameters, e.g. laser power density, laser beam scanning speed and powder flow rate, to obtain crack free and WC_p containing surface layer, has been examined. Before the injection of ceramic particles into remelted surface layer, the influence of processing parameters of laser surface remelting on the microstructure and properties of selected duplex steels was also investigated. Although after simple laser surface remelting the austenitic phase is almost not present inside remelted layer, in the case of LMI the austenite was observed in vicinity of WC particles, due to increase of carbon content acting as austenite stabilizer. The diffusion of carbon in the reaction zone results also in a formation of W₂C phase in the neighborhood of WC particles with a strong orientation relationship between them. The maximum volume fraction of the particles achieved in the metal matrix composite layer was about 10% and a substantial increase in hardness was observed, i.e. 575 HV0.2 for the matrix with embedded particles in comparison to 290 HV0.2 for untreated cast duplex stainless steels.     

WCp/Ti-6Al-4V graded metal matrix composites layer produced by laser melt injection

The laser melt injection (LMI) process was explored to produce WC particles (WC_p) reinforced Ti-6Al-4V metal matrix composites (MMC). In particular monocrystalline WC powder was used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WC_p reinforced MMC. WC_p were injected into the extended part of the melt pool just behind the laser beam. The process allowed for the minimization of the WC_p dissolution caused by the direct irradiation of the laser beam, and the decomposition reaction between WC_p and Ti melt. Different parameters were applied, and a processing window of LMI was obtained. WC_p exhibit a graded distribution along the depth direction of the MMC layer. New phases such as TiC and W₂C are observed in the MMC layer, in which TiC is the predominant phase. TiC grains present a continuous decrease in both amount and size with the distance from the surface to the bottom of the MMC layer. Two types of reaction layers around WC_p can be distinguished, namely an irregular reaction layer and a cellular reaction layer. The growth and final morphology of reaction layers are most likely being dominated by the composition of the neighbouring melt pool. A gradual hardness distribution in the depth direction of the composites layer is observed. Moreover, the transition from the MMC layer to the substrate also exhibits a gradual change in the hardness.     

Sliding wear resistance of TiCp reinforced titanium composite coating produced by laser cladding

Titanium metal matrix composite coatings (MMC) are considered to be important candidates for high wear resistance applications. Laser cladding (LC) by coaxial powder feeding is an advanced coating manufacturing process, which involves laser processing fine powders into components directly from computer aided design (CAD) model.In this study, the LC process was employed to fabricate TiC particle reinforced Ti6Al4V MMC coatings on Ti6Al4V hot rolled samples.The experimental results show that during LC process, TiC particles are partially dissolved into melted Ti-base alloy and precipitated in the form of TiC dendrites during cooling.Dry sliding wear properties of these MMC layers have been compared with substrate materials wear. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show improved tribological properties connected with the TiC_p addition and the LC process parameters.     

Performance of a cutting tool made of steel matrix surface nano-composite produced by in situ laser melt injection technology

Steel-matrix (105WCr6 steel) surface nano-composites with (Ti,W)C micron-sized and (Fe,W)₆C nano-sized carbide precipitates were produced by in situ laser melt injection technology with subsequent heat treatment. The microhardness of a 1 mm thick nano-composite layer was found to be higher than that of the initial matrix. The machinability of the surface nano-composite by a cubic boron nitride (CBN) wheel was found lower, but still reasonable compared to the initial matrix. Cutting tools produced from our new nano-composite by the CBN wheel were found to have higher wear resistance, longer tool life and provided lower cutting forces against a C45 steel workpiece compared to the initial matrix of the nano-composite.     

Microstructures and wear resistance of large WC particles reinforced surface metal matrix composites produced by plasma melt injection

Large WC particles (− 840 μm-+ 420 μm) reinforced surface metal matrix composites (SMMCs) were produced using plasma melt injection (PMI) process on a Q235 (similar to ASTM A570 Gr. A) low carbon steel substrate. Microstructures of the SMMC were observed using scanning electron microscope (SEM), and the composition was determined with energy dispersion spectroscopy (EDS). Phases were analyzed with X-ray diffraction. Micro-hardness of the SMMC was tested. Wear losses of the SMMC layer were evaluated under dry friction conditions and compared with those of the substrate material. The results show that the large WC particles are caught by crystallized metal and stay in the upper part of the SMMC layer, and there is only a little melting on the outer surface. No sinking down of WC particles occurs. The SMMC layer is well bonded to the substrate, and the interface is crack free. The wear resistance of the Q235 substrate is greatly improved with large WC particles injected.     

Microstructure and wear properties of TiC/FeCrBSi surface composite coating prepared by laser cladding

Titanium carbide particles reinforced Fe-based surface composite coatings were fabricated by laser cladding using a 5 kW CO₂ laser. The microstructure, phase structure and wear properties were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction, as well as dry sliding wear test. The results showed that TiC carbides were formed via in situ reaction between ferrotitanium and graphite in the molten pool during the laser-clad process. The morphology of TiC is mainly cubic and dendritic form; and the TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phases. The coatings reinforced by TiC particles revealed higher wear resistance and lower friction coefficient than that of the substrate and FeCrBSi laser-clad coating.     

Enhancement of abrasion and corrosion resistance of duplex stainless steel by laser shock peening

The results for laser shock peening of duplex stainless steel (22% Chromium-5% Nickel) using a pulsed Nd:YAG laser (wavelength = 532 nm, pulse width = 8 ns) for the application to high-capacity pumps for reverse-osmosis type seawater desalination plants are reported. By properly selecting the process parameters such as laser intensity of 10 GW/cm², laser pulse density of 75 pulse/mm², and 100 μm thick aluminum foil as a protective coating layer, wear volume and corrosion rate of duplex stainless steel could be reduced by 39% and 74.2%, respectively. The number and size of corrosion pits produced on wear track during copper accelerated acetic acid salt spray test decreased approximately by half as a result of laser shock peening. It is shown that laser shock peening is a practical option to improve abrasion and corrosion properties of a seawater desalination pump parts.     

Preparation and tribological properties of thin oxide coatings on an Al383/SiO2 metallic matrix composite

A new Al383/SiO₂ metal matrix composites (MMC) was designed to improve the wear properties of the aluminium (Al) alloys with manufacturing cost much lower than the hypereutectic Al-Si alloys. However, like the hypereutectic Al alloys, the MMC was also subject to large plastic deformation of the soft Al matrix under high contact stress during lubricated sliding wear tests. As a result, the reinforced SiO₂ particles detached from the matrix and promoted the third-body wear. In this paper, to improve the wear performance of the MMC under high contact stress but also to avoid the honing process, a new proprietary approach based on a modified Plasma Electrolytic Oxidation (PEO) process was used to produce oxide coatings on the MMC. The effect of both oxide coating thickness and the volume content of SiO₂ particles on the wear behaviour of the MMC was investigated. It was found that with a proper combination of the volume content of SiO₂ and coating thickness, the coated MMC presented a much higher wear resistance and lower friction coefficient than the uncoated MMC.     

Microstructure and wear properties of aluminum/aluminum-silicon composite coatings prepared by cold spraying

Composite coatings containing aluminum and aluminum-11.6 wt.% silicon eutectic alloy phases of varying compositions were fabricated using cold spraying. Coating contained a uniform distribution of the two phases. The hardness of the coatings increased as the volume fraction of Al-Si in the coating increased. The length to width ratio of the splats was found to be larger for Al particles compared to Al-Si particles. Dry sliding ball-on-plate wear tests indicated that the wear volume loss was similar for the Al and Al/Al-Si composite coatings in spite of the increase in microhardness. This discrepancy is explained by the inter-splat delamination mechanism. The coefficient of friction of aluminum coating reduced on Al-Si addition.     

The direct laser deposition of AISI316 stainless steel and Cr3C2 powder

The laser deposition of AISI316 powder blended with Cr₃C₂ over austenitic stainless steel plate was carried out as part of an investigation aimed at determining the feasibility of applying localized reinforcement to stainless steel components. The chromium carbide powder dissolved in the process to produce a range of carbides which reinforced and increased the hardness of the material. The results of optical microscope metallography and SEM/EDX and XRD analysis as well as microhardness measurements are reported. Surfaces produced by deposition of the powder blend were machine-ground and subjected to pin-on-disc and corrosion tests. The tests indicated an improvement to sliding wear resistance and a good resistance to salt spray and pitting corrosion conditions.     

Tribological evaluation of Fe-B-TiB2 metal matrix composites

Iron and titanium borides have been widely used for the production of metal matrix composites (MMC). The majority of the studies focus on the Fe-TiB₂ and/or the Fe-TiB₂-TiFe₂ region of the ternary Fe-Ti-B diagram, whereas the Fe-TiB₂-Fe₂B area has not yet been systematically studied, although it combines two very hard particles, namely TiB₂ and Fe₂B. This research deals with the wear behavior and tribological evaluation of Fe₂B-TiB₂ MMC layers, which were successfully produced on the surface of plain carbon steel, using the plasma transferred arc (PTA) technique. The counterbody, either tool steel or alumina ball, plays an important role in the wear rate and friction coefficient of the boronized surfaces. The “free” boron content in the Fe-TiB₂-B system, i.e. boron not bound in TiB₂, affects the tribological behavior of the alloyed layers. With steel as the counter-body material, “free” boron content increases the wear rate due to the formation of a more brittle matrix which is easily removed by adhesion, while with the alumina counter-body it has the tendency to decrease the wear rate, as the strengthened matrix can resist better to abrasion. The friction coefficient values for the tool steel ball are smaller than those of the alumina ball, owing to the different wear mechanisms involved.     

Hydrogen storage properties of MgH2/SWNT composite prepared by ball milling

A systematic investigation was performed on the hydrogen storage properties of mechano-chemically prepared MgH₂/single-walled carbon nanotube (SWNT) composites. It is found that the hydrogen absorption capacity and hydriding kinetics of the composites were dependent on the addition amount of SWNTs as well as milling time. A 5 wt.% addition of SWNTs is optimum to facilitate the hydrogen absorption and desorption of MgH₂. The composite MgH₂/5 wt.% SWNTs milled for 10 h can absorb 6.7 wt.% hydrogen within about 2 min at 573 K, and desorb 6 wt.% hydrogen in about 5 min at 623 K. Prolonging the milling time over 10 h leads to a serious degradation on hydrogen storage property of the MgH₂/SWNT composite, and property/structure investigations suggest that the property degradation comes from the structure destruction of the SWNTs.     

Fabrication of free standing 316-L stainless steel–Al2O3 composite micro machine parts by soft moulding

This paper presents a successful method for fabricating high-quality stainless steel–alumina composite micro machine parts using a soft moulding technique. The fabrication process starts with the production of SU-8 master moulds using a photolithography technique, followed by mirror replication of PDMS soft moulds, preparation of composite slurry using superfine 316-L stainless steel (5 μm) and α-alumina powder (400 nm) in 2.5, 5, 7.5 and 10 wt.%, filling the moulds, obtaining the green parts, debinding and sintering. The fabrication process was investigated in detail and the optimum dispersant and binder was obtained. The process resulted in high-quality composite micro parts that retain the very detailed features of the SU-8 master moulds. The density and micro hardness of the sintered parts were also investigated for the different composite compositions. The hardness of the stainless steel composite was improved by about 1.8 times that of the pure 316-L stainless materials by the addition of 10% alumina.     

High power diode laser treatments for improving corrosion resistance of A380/SiCp aluminium composites

Laser surface melting (LSM), using a high power diode laser, was used to modify the electrochemical behaviour of A380/SiC/xxp aluminium composites in aerated 3.5 wt.% NaCl solution. Corrosion mechanism was determined by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM) and low-angle X-ray diffraction (XRD). Laser-treated surface revealed a refined microstructure with homogeneous microdendrites, good matrix/reinforcement bonding and absence of cathodic intermetallic compounds. As a result, laser treatment increased the surface hardness and reduced localised corrosion attack.     

Formation of WC-iron silicide (Fe5Si3) composite clad layer on AISI 316L stainless steel by high power (CO2) laser

An attempt was made to produce WC-iron silicide cladded layer on AISI 316L stainless steel by laser processing to obtain high hardness and lesser variations in hardness distribution in the layer. Different compositions of coating materials (WC, Si and Ni) and laser processing parameters were used. A good and defect free cladded layer of WC-iron silicide was obtained for an energy density of 22.5 J/mm² and coating composition of 40WC-40Si-20Ni (wt.%). The layer exhibited average hardness of about 883 HV with lesser variations in the hardness distribution and also higher wear resistance compared to the substrate.     

Fabrication and wear characteristics of MoSi2 matrix composite reinforced by WSi2 and La2O3

MoSi₂ matrix composites (RWM) reinforced by the addition of both WSi₂ and La₂O₃ were fabricated by mechanical alloying and self-propagating high-temperature synthesis (SHS) technique. This composite was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is difficult to synthesize RWM composite by mechanical alloying with Mo–W–Si–La₂O₃ powder mixture, and suitable by self-propagating high-temperature synthesis. The hardness and toughness of MoSi₂ was improved significantly by the addition of both, WSi₂ and La₂O₃ more than by only WSi₂. By adding 0.8 wt.% La₂O₃ and 50 mol.% WSi₂ into the MoSi₂ matrix, this composite has the highest hardness and toughness and exhibits more wear resistance than monolithic MoSi₂ during the sliding wear test under oil lubrication, in this case, the material removal mechanism has been observed to be micro-cutting and micro-fracture.     

Microstructure and tribological behaviour of nano-structured metal matrix composite boride coatings synthesized by combined laser and sol-gel technology

Hard nano-structured metal matrix composite (MMC) boride coatings have been synthesized by laser melting of pre-placed powder mixture paste of B₄C + sol-gel derived nano-particulate TiO₂ on AISI 1050 (EN43) medium carbon steel and AISI 316L stainless steel substrates. Different coating/processing gas conditions were employed to understand the influence of graphite and nitrogen gas interactions with the coating material at high temperatures. Laser synthesized coatings were characterized by SEM, EDX, FEGSEM, XRD and HRTEM. Results show that it is possible to synthesize nano-structured MMC coatings (with TiB₂ and TiB particulates in the ranges of 5-10 nm, 20 nm and 200-500 nm) by employing the combined laser and sol-gel route. Nano-particulate and sub-micron level TiB and TiB₂ are found dispersed throughout the metal matrix. Other borides and carbides are present in micro-level patches dispersed in a eutectic matrix. Hardness of the composite coatings is in the range 800-2000 HV_0.1. The minimum coefficient of sliding friction obtained in a pin-on-disc set-up was 0.35 (against cemented tungsten carbide) while wear rates (against diamond) were substantially improved (up to 5 fold reduction) over that of the substrates.     

The in situ synthesis and wear performance of a metal matrix composite coating reinforced with TiC-TiB2 particulates, formed on Ti-6Al-4V alloy by a low oxygen partial pressure fusing technique

A metal matrix composite coating reinforced with TiC-TiB₂ particulates has been successfully fabricated utilizing the in situ reaction of Al, Ti and B₄C by the low oxygen partial pressure fusing technique to improve the wear resistance of Ti-6Al-4V alloy. The results show that increasing the B₄C content is adverse to forming the coating for the formation of interfacial stress; however, the addition of TiC powder as a diluent can favor the formation of this coating and the addition of small amounts of Y₂O₃ can greatly improve the adhesion of the coating. After a pin-on-disc wear test, the wear mass loss of the coating is only about 1/12 that of the Ti-6Al-4V alloy and the wear mechanism of coating is a mixed type of slight peeling-off, adhesion and abrasion.