► Responses of SLM-produced and wrought Ti6Al4V to heat treatment are compared. ► Temperature is found to be the controlling parameter for treatments in the α+β range. ► Ductility could be improved ...by a factor of 85%, from 7.27% to 13.59%. ► An optimal heat treatment for SLM produced Ti6Al4V is proposed.
The present work shows that optimization of mechanical properties via heat treatment of parts produced by Selective Laser Melting (SLM) is profoundly different compared to conventionally processed Ti6Al4V. In order to obtain optimal mechanical properties, specific treatments are necessary due to the specific microstructure resulting from the SLM process. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, the effect of several heat treatments on the microstructure and mechanical properties of Ti6Al4V processed by SLM is studied. A comparison is made with the effect of these treatments on hot forged and subsequently mill annealed Ti6Al4V with an original equiaxed microstructure. For SLM produced parts, the original martensite α′ phase is converted to a lamellar mixture of α and β for heat treating temperatures below the β-transus (995°C), but features of the original microstructure are maintained. Treated above the β-transus, extensive grain growth occurs and large β grains are formed which transform to lamellar α+β upon cooling. Post treating at 850°C for 2h, followed by furnace cooling increased the ductility of SLM parts to 12.84±1.36%, compared to 7.36±1.32% for as-built parts.
Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. This review ...article first provides a summary of fundamental theoretical aspects of microwave and microwave hybrid sintering, and then advantages of microwave sintering against conventional methods are described. At the end, some applications of microwave sintering are mentioned which so far have manifested the advantages of this novel method.
Al-Zn-Mg-Cu alloys (7xxx series Al alloys) are extensively used for their superior mechanical and corrosion performance. These properties are microstructure-sensitive and highly dependent on the ...formation, growth and coarsening of precipitates. To date, a wide variety of ageing procedures have been developed to tailor the evolved microstructures so as to yield a good combination of mechanical capacity and corrosion resistance of 7xxx series Al alloys. Among these methods, isothermal ageing, multi-stage ageing, non-isothermal ageing, retrogression and re-ageing (RRA), and stress ageing (i.e. creep ageing) are the most significant. In the present review, all of these approaches are comprehensively introduced and their potential effects on the microstructure and properties of Al-Zn-Mg-Cu alloys are fully reviewed. Also, recent advances and future prospect in this field are addressed.
As one of the most important engineering materials, aluminum alloys have been widely applied in many fields. However, the requirement of enhancing their mechanical properties without sacrificing the ...ductility is always a challenge in the development of aluminum alloys. Thanks to the excellent physical and mechanical properties, graphene nanoflakes (GNFs) have been applied as promising reinforcing elements in various engineering materials, including polymers and ceramics. However, the investigation of GNFs as reinforcement phase in metals or alloys, especially in aluminum alloys, is still very limited. In this study, the aluminum alloy reinforced by GNFs was successfully prepared via powder metallurgy approach. The GNFs were mixed with aluminum alloy powders through ball milling and followed by hot isostatic pressing. The green body was then hot extruded to obtain the final GNFs reinforced aluminum alloy nanocomposite. The scanning electron microscopy and transmission electron microscope analysis show that GNFs were well dispersed in the aluminum alloy matrix and no chemical reactions were observed at the interfaces between the GNFs and aluminum alloy matrix. The mechanical properties׳ testing results show that with increasing filling content of GNFs, both tensile and yield strengths were remarkably increased without losing the ductility performance. These results not only provided a pathway to achieve the goal of preparing high strength aluminum alloys with excellent ductilitybut they also shed light on the development of other metal alloys reinforced by GNFs.
•PM 6061 Al alloy MMCs containing 500nm SiC particles were prepared.•Industrial high energy ball milling and HIP as primary process was used.•SiC nanoparticles were homogeneously distributed after ...extrusion.•Improvements in Young’s modulus, strength and toughness were obtained.•Heat treatment produces a higher increment in the MMC strength the higher the vol% nSiC.
Materials with high specific strengths as well as damage tolerance are of great importance for automotive and aerospace applications. Ceramic reinforced metal matrix composites (MMCs) show good potential for these uses but have been hampered by insufficient ductility and production issues, both of which this work looks to resolve. Nanoparticle reinforced 6061 aluminium alloy matrix composites have been produced by a powder metallurgy route and shown to exhibit high strength and Young’s modulus alongside good ductility and low density.
A powder metallurgy route consisting of high energy ball milling, hot isostatic pressing (HIP) and extrusion has proved a highly effective process for achieving a homogeneous distribution of particles, with minimal clustering of the nanoparticles, at an industrially relevant scale. After heat treatment the composites display high strengths, owing to SiC nanoparticle reinforcement as well as the age hardening effect. The remarkable feature of nanoparticle reinforced MMCs compared to micron size reinforcements is that particle fracture does not occur and effective particle–matrix bonding can be taking place, resulting in a greater combination of strength and toughness.
The combination of properties achieved by the composites studied in this work are superior to most of the micron sized particle reinforced MMCs reported elsewhere and are well beyond what is possible with traditional aluminium alloys.
Aluminum and magnesium are two highly important lightweight metals used in automotive applications to reduce vehicle weight. Crystallographic texture engineering through a combination of intelligent ...processing and alloying is a powerful and effective tool to obtain superior aluminum and magnesium alloys with optimized strength and ductility for automotive applications. In the present article the basic mechanisms of texture formation of aluminum and magnesium alloys during wrought processing are described and the major aspects and differences in deformation and recrystallization mechanisms are discussed. In addition to the crystal structure, the resulting properties can vary significantly, depending on the alloy composition and processing conditions, which can cause drastic texture and microstructure changes. The elementary mechanisms of plastic deformation and recrystallization comprising nucleation and growth and their orientation dependence, either within the homogeneously formed microstructure or due to inhomogeneous deformation, are described along with their impact on texture formation, and the resulting forming behavior. The typical face-centered cubic and hexagonal close-packed rolling and recrystallization textures, and related mechanical anisotropy and forming conditions are analyzed and compared for standard aluminum and magnesium alloys. New aspects for their modification and advanced strategies of alloy design and microstructure to improve material properties are derived.
For conventional titanium matrix composites (TiMCs), there is always a trade-off issue between enhanced strength and ductility of these materials. In this study, we explore a new design methodology ...by reinforcing titanium alloy matrix with carbonaceous nanomaterials and investigate the mechanisms for achieving a good balance of their strength and ductility. The TiMCs were synthesized through a low-cost powder metallurgy route using pre-mixed Ti-6Al-4V (TC4) powders and various carbon based nanofillers, including graphite powders (GPs), graphene oxide nanosheets (GONs) and graphene nanoplates (GNPs), and were further rolled at a temperature of 1173 K with a deformation of 66.7%. Among these three types of carbon reinforcing sources, the GNPs are more easily reacted with TC4 matrix and form more contents of TiC phases after sintering owing to their larger amounts of defects than those of the GPs and GONs. TiC products are identified to play a bridging role for not only connecting the TC4 matrix but also forming coherent interfaces with the TC4 matrix, thus facilitating a strong interfacial bonding of the composites. The as-rolled GNPs/TC4 composites exhibit a 0.2% yield strength of 1146.36 MPa (with an elongation of ∼8.1%), which is 24.6%, 9.22% and 5.62% higher than those of pure TC4, GPs/TC4 and GONs/TC4 composites. The GNPs/TC4 nanocomposites show a better balance of strength and ductility than those of the other two types of nanocomposites. The synergetic strengthening mechanisms are identified to be Orowan strengthening effect, effective load transfer capability of GNPs, and in-situ formation of interfacial TiC structures, which provide optimum interfacial microstructures to achieve good mechanical properties of the TiMCs.
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An addition of ≤0.5wt% lanthanum boride (LaB6) to powder metallurgy commercially pure Ti (CP-Ti), Ti–6Al–4V and Ti–10V–2Fe–3Al (all in wt%) resulted in improved sintered density, substantial ...microstructural refinement, and noticeably increased tensile elongation. The addition of LaB6 led to scavenging of both oxygen (O) and chlorine (Cl) from the titanium powder during sintering, evidenced by the formation of La2O3 and LaClxOy. The pinning effect of La2O3, LaClxOy and TiB inhibited prior-β grain growth and resulted in subsequent smaller α-laths. The formation of nearly equiaxed α-Ti phase is partially attributed to the nucleation effect of α-Ti on TiB. The improved sintered density was caused by B from LaB6 rather than La, while excessive formation of La2O3 and TiB with an addition of >0.5wt% LaB6 resulted in a noticeable decrease in sintered density. The improved tensile elongation with an addition of ≤0.5wt% LaB6 was mainly attributed to the scavenging of oxygen by LaB6, partially assisted by the improved sintered density. However, an addition of >0.5wt% LaB6 led to the formation of large La2O3 aggregates and more brittle TiB whiskers and therefore decreased tensile elongation. Balanced scavenging of O is thus important. The optimal addition of LaB6 was 0.5wt% but this may change depending on the powder size of the LaB6 to be used.
This study aims to investigate the role of graphene on wear and corrosion behaviors of pure magnesium. Magnesium/Graphene Nanoparticle (GNP) composites were fabricated via semi powder metallurgy ...method with a different content of graphene (0.1, 0.25 and 0.5 wt%). The effect of graphene in pure magnesium was examined by hardness, wear and corrosion tests. Microstructural and phase analysis were carried out by Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analysis. Experimental results revealed that, hardness values increased with the addition of graphene. There was a same trend in wear behaviors with increase of graphene rate. The best wear performance was belonging to the 0.50 wt% graphene/mg composite under load of 10N. So improvement of wear properties was achieved using graphene as reinforcement. According to the microstructural evolution, the uniform distribution was achieved for all samples but partially agglomeration could be seen in Mg-0.50 wt% graphene. Compared to the pure magnesium, corrosion performance was affected negatively in graphene reinforced composites.
•Graphene reinforced was used as a reinforcement with different content (0.1,0.25,0.5 wt%) for magnesium matrix composite.•Composites were produced by semi powder metallurgy method that is based on solution.•Mechanical properties of pure magnesium were improved with the addition of graphene.•Wear resistance was enhanced directly with graphene content.•Graphene has negative effect for corrosion performance of magnesium.
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