Search

This research work aims to investigate the aluminum and silicon alloy reinforced with the ZrO2 powder particles, which has been fabricated using stir casting and spray deposition method. The mechan...

Spray-forming Al–Cu–Mg alloy was compressed to 70% deformation at 300–450 °C and strain rates of 0.01–10.00 s−1 on a Gleeble-3180 system. The microstructures of the hot deformed, sprayforming, nano-sized Al–Cu–Mg alloys were studied through electron backscatter diffraction. Constitutive equation and parameter Z were established to describe the deformation behavior of the alloy at high temperature, and the Q value was 155.67 KJ·mol−1. 3D power dissipation and processing maps were analyzed under strain values of 0.3, 0.6, 0.9, and 1.2. When the strain was increased from 0.6 to 0.9, the processing performance changed remarkably. Dynamic recovery occurred at low temperature and high strain rate, whereas dynamic recrystallization took place at increased temperature and low strain rate. The region in 400–450 °C and 0.01 s−1–0.08 s−1 exhibited an improved processing performance.

In the present study, the microstructural characteristics, compressive strength, and corrosion behavior of aluminum-cenosphere composite foam (CF) developed by spray forming route (processed with 5 Psi (3.45 × 104 N/m2) and 10 Psi (6.90 × 104 N/m2) hydrogen pressure) has been undertaken. The microstructure of the spray-formed coupon consists of hollow cenosphere particles distributed uniformly in aluminum matrix. Compressive yield strength (YS) of the aluminum-cenosphere foam (CF) is different from commercially pure aluminum (cp-Al). It is found that the YS of the foam processed with 5 Psi is 83.62 MPa and for the foam processed at 10 Psi is 113.32 MPa as compared to 104.42 MPa for cp-Al. A detailed study of corrosion behavior through electrochemical measurements indicates that CF exhibits a reduced corrosion rate from 0.092 (for cp-Al) to 0.056 mm/year and 0.080 mm/year for the samples processed with 10 and 5 Psi, respectively. Through a detailed analysis of Nyquist and Bode plots derived from EIS measurements, it is concluded that mostly localized corrosion occurs in all the samples. The post-corrosion microstructural study confirms that interface of aluminum and cenosphere is the potential area for initiation of corrosion.

The spray forming technique is one of the emerging technologies that exhibit the near net shape forming capability of materials with improved mechanical and tribological properties, which enhance the performance of the material. This technique has the relatively high rate of deposition and solidification, which provides the fine size particles and their minimum segregation. Economically benefited, single step spray forming technique is a flexible and wide range of materials can be produced that are not feasible by any other techniques. This review paper provides the overview of spray forming technique to produce aluminium matrix materials. The major focus has been given to (a) microstructural features, (b) influence of process parameters, (c) porosity formation and its control and (d) evolution of mechanical and tribological properties. This review will be conclude the further recommendation for new research and direction to produce aluminium matrix materials for different applications.

This paper presents the study of the microstructure, wear properties of spray-deposited and hot compressed Al-35Si and Al-45Si alloys. The microstructure analysis and wear mechanisms of spray forme...

Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated (solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 °C, imparting higher tensile (586 MPa) and fatigue (198 MPa) strengths.

In the present study, the microstructure and tribological performance of Al alloy has been enhanced by cryorolling. The Al-6 wt.% Si alloy has been selected as Al alloy which has been prepared by spray forming technique with 400 mm flight distance. Developed spray formed Al alloy has been subjected to cryorolling with different thickness reduction (25% and 50%) on non-reversing rolling mill using liquid nitrogen. The alteration in microstructure and tribological properties has been studied by different techniques. The microstructure results indicate that the cryorolling process refines the size of aluminium rich phase and silicon particles of spray formed Al alloy. The tribological testing results illustrate that the wear rate of Al alloy decrease by cryorolling. While the cumulative volume loss and wear rate increase with an increasing sliding distance and applied load for spray formed and cryorolled Al alloy. The coefficient of friction exhibits a fluctuating action with sliding distance while it decreases with an applied load and cryorolling. The worn surfaces have also been analyzed under scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM) techniques to study the operative wear mechanisms. Hardness property and microscopic analysis of Al alloy have also been correlated with tribological properties.

The effect of different fabricating processes (spray forming and conventional casting) and homogenization treatment on the microstructure of an 7055 alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron probe X-ray micro-analyzer (EPMA), and transmission electron microscopy (TEM). It was found that the grain size of the as-deposited (spray formed) 7055 alloy had half the size as that of the as-cast 7055 alloy and there was no Al2CuMg phase that embedded in the coarse Mg(Zn, Cu, Al)2 phase distributed along the grain boundaries in the as-deposited 7055 alloy. No segregation of zirconium was observed in the as-deposited 7055 alloy. After homogenization heating at 350 °C/5 hours + 470 °C/24 hours, Al3Zr dispersoids were inhomogeneously distributed within grains in the traditionally cast 7055 alloy, while more homogeneously distributed within grains in the spray-formed 7055 alloy. Compared with the traditional cast 7055 alloy, the uniform distribution of Al3Zr dispersoids in the spray-formed 7055 alloy retards recrystallization more effectively. This investigation highlights the advantage of spray forming technology on improving microstructure of a 7055 alloy.

Twin fluid atomizers allow for two different spray forming modes, flow focusing and flow blurring, depending on the operating, geometric, and thermophysical properties of the working liquids. In flow focusing mode, the liquid jet breaks outside the injector, whereas in flow blurring mode, the liquid jet breaks inside the atomizer. Operating conditions are believed to play an essential role in determining the size and velocity of droplets with specific geometric and fluid properties. This work investigates the effect of air flow rate and liquid flow rate on spray characteristics by varying them independently. The geometric parameters, height (H = 0.3 mm) and orifice diameter (D = 1.5 mm) of the atomizer are kept constant (with H/D = 0.2). Spray mode is identified using high-speed images. Phase Doppler particle analyzer is used to measure droplet size and velocity simultaneously. Regardless of liquid flow rate, flow focusing mode is observed at low air flow rate and flow blurring mode is observed at high air flow rate. In general, flow blurring mode produced smaller droplets at higher velocities than flow focusing mode. The Joint probability distribution function of droplet size and velocity shows unimodal near the exit of the atomizer and bimodal distribution around 50 mm downstream due to the completion of the secondary breakup around that position and the subsequent loss of momentum due to the resistance of the surrounding air from the injector outlet. Flow focusing mode showed that sauter mean diameter and mass median diameter tend to increase initially due to coalescence of the spray and begin to decrease due to secondary breakup. The joint probability distribution of droplet Weber number and the droplet Reynolds number indicate that the flow blurring spray produced finer and faster droplets than the flow focusing spray. Overlapping of two Gaussians representing smaller and larger droplets best fits the droplet probability distribution as compared to lognormal or gamma or beta distribution.

Recently it was shown that the Al–Cu–Fe–Cr system can form a microstructure consisting mainly of quasicrystalline and α-Al phases by arc-melting and subsequent annealing of an appropriate composition. In the present work we demonstrate that it is possible to fabricate a large volume of this composite directly from the liquid phase by spray forming an Al85Cu6Fe3Cr6 (%at) alloy. The overspray powder and an arc-melted sample were also analyzed. Tribological properties of the Al-based composite reinforced with quasicrystals was evaluated by pin-on-disk tests, which demonstrated to be superior than an Al–Si alloy, A380, used in this work as a comparison material.

In this research, the effects of solid solution, peak aging (PA), over aging (OA) and retrogression re-aging (RRA) on microstructure, mechanical properties, and corrosion resistance of the spray-formed Al–Zn–Mg–Cu alloy were systematically and comparatively studied. It was found that after solid solution, most of the secondary phases dissolved into the α(Al) matrix and created a favorable condition for aging treatment. When the material was subjected to the RRA, the microstructure of the alloy consisted of fine precipitates within the grains similar to the PA condition and discontinuous coarse precipitates along the grain boundaries resembling the OA condition, allowing the RRA specimens to possess optimal strength (747 MPa) and high intergranular corrosion (IGC) resistance. The mechanism of IGC on mechanical properties on different aged samples was elaborated.

Cast Al(5.5 to 6.3 wt pct)Si-(3.1 to 3.7 wt pct)Cu alloys containing 0.6 and 1.2 wt pct Fe were processed by spray forming, rotary swaging, and homogenization/solution heat treatment, which led to a tensile ductility of 16 pct. Such outstanding ductility is ascribed to the microstructure formed: globular silicon particles, refined iron-rich intermetallics, and a supersaturated solid solution of Cu in the α-Al matrix that promoted dynamic strain aging and homogenization of the deformation process.

The present paper describes the Lead dispersion in hypoeutectic Aluminium-Silicon alloys and their microstructural characteristics. The homogeneous dispersion of Lead (Pb) in Aluminium-Silicon alloys (Al-6Si+Pb (=0, 10, 15, 20, 25)) were fabricated by using of spray forming technique (also known as spray casting or spray deposition) in the form of near-net shape disc. The microstructural characterization has been done for different location of spray formed disc by using optical microscopy (OM), Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) respectively. The results of the optical image were exhibited the equiaxed and globular grain morphology of primary Aluminium with the homogeneous dispersion of extremely fine and malleable particles of Lead and spherical particles of silicon in α–Aluminium matrix. The dispersed Lead has seen clearly in the SEM images of spray formed Aluminium-Silicon alloys and result of XRD pattern confirmed the phases of Aluminium-Silicon and Lead. The grain size of Aluminium has been analyzed by intercept line method. The lattice parameter and lattice strain have been calculated with the help of the XRD pattern to determine the effect of Lead dispersion on Al-Si alloy.

Al-4.5 wt% Cu alloy deposit was produced through spray forming process for the spray height of 400 mm. The atomization and deposition process was carried out under (nitrogen) inert gas atmosphere. Microstructure of the spray deposit was studied from centre of the deposit to the peripheral region of the deposit. Densities of the sample at 3 different locations from the centre are 2.42, 2.38 and 2.25 g/cc. The grain size of the spray deposit is measured by using are found to be 29, 24, 20 μm at 3 different locations a, b and c from the centre of the deposit. The percentage of porosity is measured from the image analysis. The percentage of porosity at 3 different locations a, b & c were found to be increased by 3, 6 and 12% respectively. The Vickers hardness of the spray formed samples for 3 different locations was 446, 462 and 478 MPa.

In the present investigation, Influence of rolling on wear and friction behavior of Al alloy composite has been studied. The composite, namely Al-Si alloy reinforced with graphite was developed through the unique spray forming route in the spray forming chamber by using N2 as an atomization gas. Developed spray formed Al alloy composite was gone through to the warm rolling with different thickness reduction ranges on non reversing rolling mill at constant temperature 250 °C. The microstructural and mechanical testing results indicate that the warm rolling of the composite increases the distribution of the graphite and silicon particles, minimizing the porosity with the refinement of α-aluminium grains of the matrix and improves the mechanical properties. The wear and friction testing results indicate that with an increase in sliding distance, volume loss of the composite with all rolling reduction increases. Similar kind of behaviour is also observed between the wear rate and applied load. However, with the rolling reduction, the wear rate of the composite decreases. In spite of that, the average coefficient of friction decreases with an increasing the applied load and the rolling reduction of the composite while it shows a fluctuation tendency with the sliding distance. The surfaces after the wear tests are also studied under the different surface characterization techniques to quantify the surface parameter and the operative wear mechanisms. The tribological properties are also correlated with the microstructural properties of the composite with different rolling reduction.

The forming of the ink droplet is very important in the inkjet control system. It is related to the forming of the ink droplet on the substrate with good printing effect. In the process can use of inkjet ink observation system to observe the ink drops of spray forming process, at the same time, use the LED flash and CCD camera to film the formation of the ink droplets, through the pictures use edge detection algorithm to analyze drops forming condition and flight path, still can use the shape of the Hough transform to detect the drops (mainly used to detect circular drops), and finally by MATLAB/Simulink simulation tool to drops control system simulation analysis, The data of ink droplet forming is analyzed and tested in the ink feeding system.

Spray forming is an advanced casting process that produces refined and homogenous microstructure directly from the liquid metal regardless of the alloy system. However, the microstructure evolution during spray forming is complex because the process comprises two sequential steps with very different cooling rates, i.e., atomization and deposition. It is well known that the microstructure of cast irons is highly dependent on the chemical composition and the cooling rate imposed to the liquid. In order to better understand the microstructural evolution during solidification by spray forming, this study investigated the solidification of two cast irons with different stable–metastable eutectic temperature interval (ΔTES−M), 30 K and 17 K. The microstructures of both overspray powders presented a dendritic array of austenite with cementite in the inter-dendritic spacing. Despite the high cooling rates imposed to the alloys during the atomization step, the final microstructure was defined by the cooling conditions prevailing during the final step of deposit solidification and stable eutectic was formed. This was ascribed to the dynamic process involving heating and remelting of the low melting temperature phases present in the droplets that arrives completely or partially solid in the deposition zone.

The present study outlines the effect of warm rolling on the Al/Graphite alloy composite to investigate its effect on mechanical performance. The Al/Graphite alloy composite has been fabricated by the spray forming process and has been subjected to the rolling at 250 °C with varying reduction. The rolled composite has been studied under different characterization techniques such as X-ray fluorescence (XRF), optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS) and tensile tester. The XRF and EDS results indicate that the Al/Graphite alloy composite is successfully formed. The microscopy results show that the grain size of α-aluminium and agglomeration of the particles refine by rolling and they continuously decrease with an increase in rolling reduction. The strength and percentage elongation of the composite improves by rolling and they continuously increase with an increase in rolling reduction. Further, the fracture surface study has also been performed and it indicates that the fracture of the composite alters from brittle to ductile mode with an increase in rolling reduction. The appeared fracture surface of the composite has also been correlated with the produced microstructure and the tensile properties.

With the increase of welding speed from 75 to 150 mm/min, the grain size of the nugget zone first decreased and then increased, and the smallest grain size was obtained at 100 mm/min. The maximum tensile strength of 445 MPa was achieved at the welding speed of 100 mm/min, equivalent to 70% of the base metal. The hardness value of the heat-affected zone increased with the rising welding speed. Joint hardness was affected by precipitated phases and it decreased overtly from thermo-mechanically affected zone to heat-affected zone. Owing to the fact that a number of big precipitates clustered in the heat-affected zone, the strengthening effect in spray formed ultra-high strength 7055 aluminum alloy was weakened which caused the hardness of the joint to reduce remarkably. Because of the recrystallization, most of the phases in nugget zone were dissolved and the rest were similar to those in the base metal, while AlCuMg phase and Al2Cu phase precipitated in heat-affected zone. The phase precipitated in the nugget zone and heat-affected zone decreased gradually with the increase of the welding speed.

A novel Si-Al alloy prepared by spray forming process investigated in this paper. Experimental results show that fine and homogeneous grain structure is obtained in as-deposited alloy. In addition,...

The Zn-rich Al-11.3Zn-2.65Mg-1Cu alloy was prepared by spray forming rapid solidification technology and then processed by hot extrusion and heat treatment to T6-temper condition. The characteristics of spray-formed and extruded materials are systematically investigated, and accordingly, solution treatment parameters are derived at an intermediate temperature. The tensile results indicate that the alloy can reach yield strength as high as 807 MPa due to massive precipitation of ή phase which is attributed to the high supersaturation of the solutionized alloy because of the cumulative effect of spray forming and optimal solution treatment.

In this investigation, the mechanical and tribological behavior of warm rolled Al-6Si-3Gr (graphite) self-lubricating composite have been studied. A spray forming process was used to synthesize the composite. The graphite particles were reinforced externally into the jet of the spray of molten Al-Si alloy. The porosity was generated under the spray forming process that was eliminated by the secondary process (warm rolling). Warm rolling was carried out with 20, 40, 60 and 80% thickness reduction in multi-passes on high non-reversing mills. Refinement and distribution of silicon and graphite particles in the composite were increased. The mechanical properties namely hardness and strengths were also improved by warm rolling. Wear properties of the composite after each thickness reduction were also investigated under dry sliding condition. Composite after warm rolling showed the better results in the coefficient of friction and wear rate. Wear properties improvement, nature of the debris particles and mechanical properties of the composite after warm rolling were discussed in details with its microstructural features. Different characterization techniques were also used to support the prediction of change in properties. The load bearing capacity of the composite was increased by warm rolling. These composites could be used for those applications where load bearing capacity and less wear is required.

7055 Al alloys samples were prepared by spray forming and hot-extrusion followed by two different aging treatment procedures. Their different distributions of GP zones, and nanoscale precipitates η...

The influence of iron additions (0.8, 1.2, and 1.5 wt.%) on the microstructure and tensile properties of the 319 aluminum alloy processed by spray forming and rotary swaging was investigated. The spray-formed deposits were rotary-swaged at 573 K with an area reduction ratio of 5:1. Room temperature tensile tests showed a substantial increase of elongation at fracture (5.5 to 8%) when compared to the values observed for the iron-containing conventionally cast counterpart (0.6%). The high values of elongation at fracture were obtained due to the significant microstructural refinement and decrease of volumetric phase fraction, especially the iron-rich intermetallics, promoted by the combination of spray forming and rotary swaging. Therefore, this processing route significantly reduces the deleterious effect on the ductility caused by the iron content and the presence of β-AlFeSi intermetallic phase in hypoeutectic Al-Si alloy.

To improve the oxidation resistance of near α-titanium alloy IMI834, TiAl-(Cr, Nb, Ta) coatings were deposited by applying high-velocity oxy-fuel (HVOF) and warm spray (WS). Comparison was made in terms of microstructure, surface morphology as well as isothermal and cyclic oxidation behaviors in the air at 750 °C up to 100 h and 100 cycles, respectively. The results show that smoother and less oxidized coatings were deposited by warm spraying. The microstructure of all coatings underwent an appreciable change during the oxidation tests, as in as-sprayed state it occurred in the nonequilibrium state. It was revealed that a small difference in the initial oxidation between the two spraying processes as well as microstructure, the level of porosity and surface roughness significantly influences the oxidation kinetics of the sprayed coatings at high temperature, which should affect the service lifetime as an oxidation-resistant layer for potential applications. After exposure at 750 °C in air, rutile TiO2 was found in addition to α-Al2O3 in the oxide scale formed on the HVOF and warm sprayed coatings. However, isothermal and cyclic oxidation tests of all WS TiAl-(Cr, Nb, Ta) coatings showed improved oxidation resistance of IMI 834 as well as good adherence to the substrate alloy.

M3:2 high-speed steel (HSS) billets with or without Nb addition were prepared by spray deposition. The effects of Nb and post-thermal-mechanical processing (decomposition treatment and hot forging), as well as heat treatment, on the microstructure and properties of M3:2 HSS were investigated. The microstructure of the as-deposited M3:2 HSS consisted of equiaxed grains with a mean size of approximately 25 µm and discontinuous plate-like M2C and irregular MC carbides distributed along grain boundaries. 0.5% Nb addition can refine the M2C plates and spheroidize MC carbides. With 2% Nb addition, the refined grains with a mean size of approximately 12 µm and continuous net of M6C and a uniform distribution of NbC carbides were obtained. The decomposition of metastable M2C carbides can be accelerated with 0.5% Nb addition due to the refined size and lower thermodynamic stability of M2C plates. With the increased degree of decomposition of M2C carbide, the M6C and MC carbides became refined and more uniformly distributed after optimal thermal-mechanical processing and heat treatment, which leads to a significant increase in bend strength and toughness.

In this study, a coating layer has been formed on a cylinder with spray forming technique by using aluminum powders which are atomized by close-coupled nozzles which have been designed and produced before. Since porosity has a major effect on the mechanical properties of spray formed parts, the effect of the parameters on the porosity has been investigated in order to have higher mechanical properties. In the experimental step, a spinning cylindrical tube was located straight forward in the atomization direction. During the experiments, the atomized aluminum powder was sprayed with the help of nozzles when they were yet in the liquid form. The cylindrical tube rotates at a different speed, and the coating has been applied from three different distances, 135, 165, and 200 mm. Therefore, a coating layer was deposited on the cylinder surface. In the study, variable protrusions of 4, 6, and 8 mm at the nozzle tip at 5, 10, and 15 bar pressure were used besides varying the spray distance. Each experimental condition was repeated three times. Samples were taken from the center and side of each coated part in order to examine their porosity, bonding with powders and substrate, powder sizes, and powder shapes using optical microscopy. The effect of newly structured grains on hardness was also examined using a microhardness tester.

Spray Forming is a material processing technology in which molten metal is transformed into near net shape solid by capturing spray of atomized metal or alloy onto a moving substrate. In the present work, performance of spray formed tool steel, H13 is investigated in terms of tensile, Charpy impact and fracture toughness properties which are then compared with that of conventional route steel. The analysis was done in two hardness ranges i.e. 44~46 HRc and 48~50 HRc. Tensile test results show that YS, UTS, %El and %RA are similar for both route materials at both hardness ranges. Charpy impact strength obtained for spray formed route steel is lower in all three directions as compared to that of conventional route steel. Fracture toughness results, at higher hardness range, show that KIC value obtained for spray formed route steel is approximately 19.5% & 33.3% lower than that of conventional route steel in LS and TS orientations, respectively. The same at lower hardness range is approximately 28.7% and 24.8% lower for spray formed route steel when compared with that of conventional rote steel in LS and TS orientations, respectively. Metallography and SEM has been done to establish reasons behind the better performance of conventional route steel.

In the present study, aluminium syntactic foam has been fabricated using cenosphere space holder by spray forming route, and its wear behavior is investigated. The microstructure of foam shows that cenosphere distributed uniformly into the matrix. Detailed investigation of reciprocating friction wear has been carried out, and finally, the fretting wear behavior of aluminium foam evaluated against tungsten carbide ball under fretting wear mode and compared with the as received commercially available aluminium. The mechanism and kinetics of wear have also been studied through a detail microstructure analysis of the worn surface. The results show that the cenosphere space holder decreases the relative density, increases the hardness and wear properties of foam compare to their solid material counterparts. Wear studies of foam show a substantial improvement in wear resistance in comparison with commercial aluminium.

LM25 alloy was obtained by the consolidated spray forming method. By using power saw the central portion was cut down into 20mmX20mm and then warm rolled with 20%,40%, 60% and 80 % at 1000c.Samples were prepared as per standards to see the microstructure by using the optical microscope. The results show that fine microstructure was observed in LM25 spray deposited Al alloy after warm rolling process due to the expediting cooling and freezing rate of spray deposit. Porosity and Mechanical properties of the warm rolled LM 25 substrate was improved than the spray casted and cold rolled.

In the present study, attempts have been made to develop aluminium foam using cenosphere as a space holder by spray forming route. The main process variables were, applied current, gas pressure, and weight fraction of space holders. Detailed investigation of the effect of process parameters on the microstructures were undertaken to optimize the processing zone for the development of foam. The mechanical properties in terms of micro hardness, compressive strength, and tensile strength have been evaluated in details. Finally, the deformation behaviour of the aluminium foam has been established.

Liquid state processing of aluminium based metal matrix nano-composites (MMNCs) along with their microstructures are reviewed critically from open literature. Results obtained by many researchers reveal that mechanical milling followed by stir casting can produce the nano-composites with reduced grain size, strong interfacial bonding and homogeneous dispersion with little agglomeration of reinforcements. Ultrasonic assisted casting reduces the agglomerations and improves wettability of the nano-particles. MMNCs with well dispersed reinforcements on the grain boundaries can be produced through induction melting process. Electromagnetic casting reduces the cracks and cavity defects; whereas spray forming and disintegrated melt deposition technique produce near-net structured MMNCs with homogeneous distribution of nano-particles. Finally, some grey area on liquid state processing of aluminium MMNCs has been identified and the scope for future research is suggested.

In many metal forming applications, especially in micro cold forming, the tools are loaded differently in various functional regions. Tailored material properties in the specific regions are therefore advantageous. To meet this requirement, different tool steels can be applied in the corresponding regions of the tools, with a good bonding in between. This kind of composite materials can be produced by means of a newly developed successive spray forming process. In addition, the different steels in the composite tools may require quite different heat treatment conditions in order to achieve the expected material properties and performance. For this purpose, a selective heat treatment based on middle frequency induction heating has been developed to austenitize the different steels at different temperatures. In this study, these two newly developed processes have been applied to produce composite tool steels for micro cold forming tools. The investigation is focused on the correlation between the processing conditions and the microstructure and properties of the composite tool steels. It shows that fine and homogeneous microstructure can be achieved in the composite tool steels, with a gradual transition of chemical and physical properties in between. The microstructure and properties of the composite tool steels are clearly correlated with their austenitization conditions during the selective induction heating.

Over the course of this paper, a FGH100L nickel based alloy, which was prepared by spray forming, had been treated by hot isostatic pressing, followed by an optimized heat treatment. The microstructure evolution of gamma prime phase under different conditions was systematically analyzed. In conclusion, both the temperature and cooling rate during the heat treatment can affect gamma prime phase on its morphology, size and distribution. By varying solution treatment temperature, size variation of γ′ phase and fine-grain microstructure was obtained at a relatively low solution treatment temperature. As for changing cooling rate, a doublet morphology of splitting γ′ phase appeared at a relatively slow cooling rate under hot isostatic pressing progress. Based on microstructural characterization of γ′ phase, the reasonable heat treatment regime of FGH100L alloy was determined. The deformation recrystallization occurred when the as-deposited alloy was treated by hot isostatic pressing, which results in grain morphology changing from spherical or sphere-like to polygon. It can be obtained multi-sized γ′ precipitates for the hot isostatic pressing alloy which treated by optimized heat treatment regime. The results indicate that the multi-sized γ′ phase microstructure is beneficial to obtain ideal comprehensive mechanical properties.

In the present study, the influence of the secondary process, namely cryorolling on microstructure, porosity and hardness of spray-formed Al–Si alloy has been studied. The Al–Si alloys included of 6 wt% of Si have been selected and have been made by the spray forming technique using nitrogen as atomized gas. Further, cryorolling of spray-formed Al–Si alloy has been performed with a different reduction on a rolling mill. The cryorolled spray-formed Al alloy with different reductions has been characterized by different techniques. The X-ray diffractometer (XRD) analysis indicates that the alloy is Al–Si alloy, and no other phases are present. However, microstructure studies indicate that the spray-formed Al–Si alloy consists of equiaxed grains of α-aluminium and Si particles, which refine by cryorolling. The porosity measurement indicates that the value of porosity decreases continuously with an increasing thickness reduction under cryorolling. The hardness has correlated with the porosity and the evolved microstructure of the Al alloy. The 50% cryorolled spray-formed Al–Si alloy exhibits the maximum improvement in properties.

An efficient spray forming technique was utilized to cast Pb-added Al-Si alloys. It was then rolled to a different percentages (0–80%) using rolling machine and microstructural characteristics as well as porosity behavior of casting alloy were systematically studied. It is noteworthy that the distribution of Pb was nearly uniform all through the aluminum phase and it was mainly at the grain boundary. Also, the grains of aluminum were found to be elongated along the rolling direction after 80% rolling. Porosity was minimum at peripheral region of the deposit and it decreased as rolling percentage is increased.

The effect of extrusion and heat treatment processes on the microstructure and mechanical properties of the spray formed 7055 alloy were systematically studied by three-dimensional X-ray microscope, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atom probe tomography and tensile testing. It was found that the main second-phases in the as-deposited 7055 alloy include θ (Al2Cu) and Mg(Zn,Al,Cu)2 phases with similar structure to the ƞ (MgZn2) phase dissolved with Al and Cu. The Al2Cu particles embedded in Mg(Zn,Al,Cu)2 phase are widely distributed on the grain boundaries. Compared with the as-cast 7055 alloy, the S (Al2CuMg) phase and T (Al2Mg3Zn3) phases were not detected in the as-deposited alloy due to the change of solidification paths caused by rapid solidification. The microporosity caused by spray forming is always observed in the as-deposited alloy, these micro-pores can be effectively eliminated by the extrusion processing. Meanwhile, compared with extrusion directly after preheating at 420 °C/24 h, additional high temperature two-stage homogenization treatment before extrusion can reduce the adverse effect of S (Al2CuMg) phase and promote the precipitation of high density of Al3Zr dispersoids, which significantly increases the recrystallization resistance and improve the mechanical properties of the alloy.

Typically, aluminum alloys are contaminated by iron during recycling cycles. Such a procedure leads to the formation of intermetallic phases with detrimental morphology, which acts as stress risers, impairing mechanical properties and consequently hindering further mechanical processing and restricting recycling. This paper aimed at studying the solidification of an AA6061 alloy highly contaminated with iron (1.4 wt%). Spray forming processing allowed altering the solidification path of the Fe-modified AA 6061 alloy, resulting in the formation of primary α-Al15(Fe, Mn)3Si2 phase with polyhedral morphology, which traps Fe and Si at elevated temperature. Furthermore, spray forming prevented the formation of intermetallic AlFeSi phases with platelet-like morphology, such as β-AlFeSi as well as the typical Chinese script morphology, resulting in a final ductile microstructure, allowing further processing by hot extrusion.

In this work, boron-modified duplex stainless steels were prepared by spray forming using design guidelines provided by thermodynamic calculations. Firstly, an investigation of stable phases and phase formation sequence in duplex steels containing high levels of boron was conducted. The calculation indicated that there was an eutectic point at around 1 wt% boron with different primary phase formations upon equilibrium solidification. For hypoeutectic compositions, the primary phase was δ-Ferrite, whereas for hypereutectic a metallic boride (M2B) should form. Additionally, eutectic reactions for both compositions should lead to the formation of borides M2B and M3B2. Secondly, spray forming experiments were conducted based on the thermodynamic calculations. Sample preparation was carried out using a conventional superduplex steel (2507) as starting material. Two different compositions were selected: one hypoeutectic (0.8 wt% B) and one hypereutectic (2.5 wt% B). The microstructural investigation revealed the formation of different types of borides embedded in an austenitic-ferritic matrix. Finally, the wear resistance was evaluated with the dry sand/rubber wheel test and a significant improvement was observed for boron-containing steels in comparison with the same steel without boron. This improvement was attributed to the presence of fine and well-distributed boride particles that protected the austenitic-ferritic matrix from material removal.

To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn2 and Al3Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation.

Ti-Al-based intermetallics are promising candidates as coating materials for thermal protection systems in aerospace vehicles; they can operate just below the temperatures where ceramics are commonly used, and their main advantage is the fact that they are lighter than most other alloys, such as MCrAlY. Therefore, Ti-Al-Si alloy coatings with five compositions were manufactured by spraying pure Ti and Al-12 wt.% Si powders using warm spray process. Two-stage hot pressing at 600 and 1000 °C was applied to the deposits in order to obtain titanium aluminide intermetallic phases. The microstructure, chemical composition, and phase composition of the as-deposited and hot-pressed coatings were investigated using SEM, EDS, and XRD. Applying of hot pressing enabled the formation of dense coatings with porosity around 0.5% and hard Ti5(Si,Al)3 silicide precipitates. It was found that the Ti5(Si,Al)3 silicides existed in two types of morphologies, i.e., as large particles connected together and as small isolated particles dispersed in the matrix. Furthermore, the produced coatings exhibited good isothermal and cyclic oxidation resistance at a temperature of 750 °C for 100 h.

Recently Cu-Al-Ni shape memory alloys have gained special attention due to their high temperature applications. This article attempts to formulate the various processing routes for processing of Cu-Al-Ni shape memory alloys such as casting route, powder metallurgy route, rapid solidification and spray forming process. The pros and cons of various processes are provided in detail. The additive manufacturing, which is an emerging process is discussed which could be a promising technique of preparing Cu-Al-Ni shape memory alloys. Further recommendations are provided in terms of producing fine-grained near net shape shape memory alloys for high temperature applications.

Throughout this project, a candidate nickel-based turbine disk superalloy was prepared by spray forming process. After creep testing, samples were carried out at 705 °C/750 MPa, 705 °C/793 MPa and 705 °C/897 MPa. The microstructure and creep properties of the alloy were investigated using transmission electron microscope (TEM). The results show that the creep rate of the alloy was improved and the creep life decreased significantly when the stress increased from 750 MPa to 793 MPa and 897 MPa. According to the result, the alloy has high stress index. Furthermore, when the stress was as relatively low as 750 MPa or 793 MPa, the creep mechanism of the alloy was dislocation shearing into γ′ phases; when the stress was as high as 897 MPa, the creep mechanism was stacking faults and micro-twins cutting γ′ phases. Under different stress conditions, the tertiary creep has a significant impact on the total deformation quantity and creep life of the alloy and the rafting of γ′ phase is the main reason of the creep acceleration. With the increasing applied stress, rafting of γ′ phase becomes obvious and it accelerates the tertiary creep deformation but reduces the creep properties of the alloy.