Effect of rotation speed and milling time to attain Nb-10Hf-1Ti alloy powders on morphology and microstructure of Nb-10Hf-1Ti powder

The mechanical alloying process was employed to produce C103 alloy with Nb-10% Hf-1% Ti (wt.%) composition using Nb, Hf and Ti powders. The mechanical alloying process was performed in an argon atmosphere in the chamber and bullets of tungsten carbide with a ball-to-powder weight ratio (BPR) of 20:1 at rotation speed of 200, 300 and 400 rpm for 2, 5 and 8 h. At rotation speeds of 200 and 300 rpm particle size decreased and became more spherical during MA. While increasing milling time at 400 rpm caused agglomeration of particles. XRD results showed that increasing milling time at a constant rotation speed has no considerable effect on reduction of crystallite size, but the lattice strain is strongly affected by it and increased obviously with further rotation speed. The results showed that the optimum milling time and rotation speed to attain Nb-10Hf-1Ti alloy powders with the least amount of contamination and appropriate morphology are 5 h and 300 rpm, respectively.     

Microstructures and mechanical properties of spark plasma sintered Cu–Cr composites prepared by mechanical milling and alloying

Nanograined Cu–8 at.% Cr composite was produced by a combination of mechanical milling (MM), mechanical alloying (MA) and spark plasma sintering (SPS). Commercial Cu and Cr powders were pre-milled separately by MM. The milled Cu and Cr powders were then mechanically alloyed with as-received Cr and Cu powders respectively. After milling, the powder mixtures were separately subjected to SPS. It was found that pre-milling Cr can efficiently decrease the size of grain and reinforcement, resulting in remarkable strengthening. The grain size of Cu matrix was about 82 nm after SPS. The Vickers hardness, compressive yield strength and compression ratio of the composite were 327 HV, 1049 MPa and 10.4%, respectively. The excellent mechanical properties were primarily attributed to dispersion strengthening of the Cr particles and fine grain strengthening of the Cu matrix. The strong Cu/Cr interface and dissolved Cr atoms can also contribute to strengthening of the composite.     

Synthesis and mechanical behavior of nanostructured materials via cryomilling

Cryomilling, the mechanical attrition of powders within a cryogenic medium, is a method of strengthening materials through grain size refinement and the dispersion of fine, nanometer-scale particles. The technique was developed as a means to decrease both the size of these particles and their spacing within a metallic matrix to increase threshold creep stress and intermediate temperature performance. More recent work has been concerned with increasing the strength of lightweight structural materials. In this overview paper, the available literature is reviewed that covers the microstructural evolution during cryomilling, consolidation and processing, the thermal stability of the microstructure, and mechanical properties of consolidated materials. The properties of cryomilled materials are compared to those results for powders and consolidated materials generated by mechanical alloying, milling at ambient temperatures and other means to produce fine grained materials.     

Effect of Y and Ce on the microstructure,mechanical properties and anisotropy of as-rolled Mg-8Li-1Al alloy

The effects of combined addition of Y and Ce on the microstructure, mechanical properties and anisotropy of as-rolled Mg-8 Li-1 Al(LA81) alloy were studied. The combined addition of Y and Ce improves the mechanical properties with a low plasticity loss by solution strengthening, dispersion strengthening,grain refinement strengthening. Mg-8 Li-1 Al-0.6 Y-0.6 Ce(LA81-0.6 Y-0.6 Ce) has better mechanical properties and shows an almost isotropy. It possesses an ultimate tensile strength of 278.7 MPa and an elongation of 15.0%. Compared to LA81 alloy, the ultimate tensile strength increases by about 17.6% with an elongation reduction of only 3.5%, and a good isotropy of ultimate tensile strength and elongation(the value of r_(avg) is near 1).     

Effects of Ag addition on microstructures and mechanical properties of Mg–6Zn–2Sn–0.4Mn-based alloy system

We investigated the effects of Ag addition on the microstructure and mechanical properties of hot-extruded Mg–6Zn–2Sn–0.4Mn-based alloys. Ag addition resulted in the formation of fine submicron-sized Mg–Ag particles, grain refinement, and weaker basal texture in the alloys. The Ag-containing extruded alloys had better mechanical properties than the alloys without Ag. The ultimate tensile strength (UTS) and elongation of alloys containing 1 wt.% Ag were 352 MPa and 19%, respectively.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of a super high strength Al–Zn–Mg–Cu aluminum alloy

Samples made of a super high strength aluminum alloy with high Zn content were friction stir welded with rotation rates of 350–950 rpm and welding speeds of 50–150 mm/min. The effect of welding parameters on the microstructure and mechanical properties was investigated. It was observed that the grain size of the nugget zones decreased with the increasing welding speed or the decreasing tool rotation rate. Most of the strengthening precipitates in the nugget zone were dissolved back and the intragranular and grain boundary precipitates in the heat affected zone coarsened significantly. The greatest ultimate tensile strength of 484 MPa and largest elongation of 9.4 were obtained at 350 rpm−100 mm/min and 350 rpm−50 mm/min, respectively. The ultimate tensile strength and elongation deteriorated drastically when rotation rate increased from 350 to 950 rpm at a constant welding speed of 100 mm/min.     

Effect of boron addition on the cavitation erosion resistance of Fe-based hardfacing alloy

The cavitation erosion behavior of Fe–Cr–C–Si–xB (x = 0, 0.3 and 0.6 wt.%) alloys were investigated up to 50 h by using 20 kHz vibratory cavitation erosion test equipment. The boron-added alloys showed the improved cavitation erosion resistance compared to the boron-free alloy. This improvement was attributed to that the boron addition enhanced the grain boundary strength and refined the grain size of the matrix. However, the cavitation erosion rate of the 0.6 wt.% boron specimen was higher than that of the 0.3 wt.% boron specimen. The higher erosion rate of the 0.6 wt.% boron was due to the larger carbide volume in the matrix.     

Thermal stability and elevated temperature mechanical properties of electroslag remelted Fe-16wt.%Al-(0.14–0.5)wt.%C intermetallic alloys

Addition of carbon in the range of 0,14–0.5 wt.% to the Fe₃Al-based intermetallic Fe-16wt.%Al (Fe-28at.%Al) alloy results in the formation of a thermally stable dispersion of Fe,AIC carbide phase. The volume fraction of these precipitates increases with increase in carbon content. Processing of these alloys through a combination of air induction melting and electroslag remelting leads to enhanced elevated temperature mechanical properties compared to those reported for the low (< 0.01 wt.%) carbon alloys with similar Al contents. Enhancement of up to 30% in elevated temperature yield strength was observed at the test temperatures (600, 700 and 800°C) used. The improvement in mechanical properties may be attributed to the presence of strengthening Fe₃AlC phase as well as the interstitial carbon present in the alloy matrix. The addition of carbon also leads to improved room temperature mechanical properties in contrast with other alloying additions (such as Mo, Ti and Si) used for enhancing elevated temperature properties of Fe₃Al-based intermetallic alloys. It is suggested that carbon may be an important alloying addition to these alloys.     

Microstructure and mechanical properties of spark plasma sintered austenitic ODS steel

In this work, austenitic oxide dispersion strengthened (AODS) steel of composition Fe–16Cr–16Ni–1.5 W–0.21Ti–0.3Y₂O₃ (wt. %) was fabricated using two–stage ball milling followed by consolidation through spark plasma sintering (SPS). In the first–stage, mechanical alloying (MA) of ferritic powder and nano sized Y₂O₃ was carried out. This was followed by the addition of Ni in second–stage milling. SPS of the milled powder was carried out at 900, 950, 1000 and 1050 °C to explore the role of SPS temperature on density, microstructure as well as mechanical properties of the consolidated samples. A relative density of ～ 99% was obtained for samples sintered at 950 and 1000 °C. The as–sintered samples were subsequently solution annealed at 1075 °C for 2 h and water quenched. X–ray diffraction studies confirmed the presence of austenite in the consolidated and solution annealed samples. Electron back scatter diffraction analysis of solution annealed samples sintered at all the temperatures revealed a bimodal microstructure. The average grain size of 1.07 ± 0.72 µm was obtained for solution annealed samples sintered at 1000 °C. Yield strength and elongation of the same was measured as 851 MPa and 18%, respectively at room temperature. These values are the best combination of strength to elongation achieved on AODS alloys processed using MA and SPS, which makes this AODS steel much promising for high temperature applications.     

Simultaneous improvement in the strength and corrosion resistance of Al via high-energy ball milling and Cr alloying

The corrosion resistance and mechanical properties of nanocrystalline aluminium (Al) and Al–20 wt.%Cr alloys, synthesized by high-energy ball milling followed by spark plasma sintering, were investigated. Both alloys exhibited an excellent combination of corrosion resistance and compressive yield strength, which was attributed to the nanocrystalline structure, extended solubility, uniformly distributed fine particles, and homogenous microstructure induced by high-energy ball milling. This work demonstrates the possibilities of developing ultra-high strength Al alloys with excellent corrosion resistance, exploiting conventionally insoluble elements or alloying additions via suitable processing routes.     

Structure and magnetic properties of nanocrystalline mechanically alloyed Fe–10% Ni and Fe–20% Ni

The mechanical alloying technique has been used to prepare nanocrystalline Fe–10 and Fe–20 wt.% Ni alloys from powder mixtures. The structure and magnetic properties were studied by using X-ray diffraction and hysteresis measurements, respectively. For both alloys studied, a disordered body centered cubic solid solution forms after 24 h milling time. The higher the milling time, the larger the lattice parameter. The steady-state grain size is ≈10 nm. The reduction of the grain size increases the saturation magnetization and decreases the coercivity. Nanocrystalline Fe–10 and Fe–20 wt.% Ni have been shown to exhibit a soft magnetic behavior.     

Effect of trace additions of Sn on microstructure and mechanical properties of Al–Cu–Mg alloys

The work is aimed at investigating the influence of trace additions of Tin (Sn) on the microstructure, mechanical properties and age-hardening behavior of Al–6.2%Cu–0.6%Mg alloy system. Al–6.2%Cu–0.6%Mg alloys containing varying weight percentages (from 0 to 0.1 wt.%) of Sn were prepared by casting technique. The mechanical properties and microstructure of these alloys were investigated in the as-cast as well as different heat treated conditions. The composition of the different phases present in the microstructure was determined by energy dispersive X-ray (EDS) analysis. The average grain size of the annealed alloy was found to be maximum with trace content of 0.06 wt.% Sn. The hardness and strength of the alloy increased but the ductility reduced with increase in Sn content up to 0.06 wt.%. Precipitation hardening behavior of the alloys was investigated by analyzing the aging time required to attain the peak hardness value. Addition of trace percentage of Sn was observed to have no significant influence on the peak ageing time of the investigated alloy system.     

Ultrafine grained copper alloy sheets having both high strength and high electric conductivity

The ultrafine grained (UFG) microstructure, mechanical properties and electric conductivity of the Cu alloys severely deformed by accumulative roll bonding (ARB) process were systematically investigated. High density of grain boundaries introduced by the ARB process has significant effect on strengthening but little effect on the electric conductivity. The UFG Cu alloys with submicometer grain sizes can achieve both superior mechanical properties and high electric conductivity.     

Mechanical properties of nanostructured Mg–5 wt%Al–x wt%AlN composite synthesized from Mg chips

In the present investigation, Mg chips are recycled to produce nanostructured Mg–5wt%Al reinforced with 1, 2 and 5 wt% nanosized AlN particulates by mechanical milling (MM). Each batch of composite mixture was milled for different milling durations to produce different degrees of grain refinement. The mechanical properties such as tensile strength, ductility and hardness with respect to the effect of grain refinement, in other words, milling duration were studied. It was found that grain size played an important role in controlling ductility of the composites.     

Preparation and structural investigation of nanostructured oxide dispersed strengthened steels

Although capability of steels has been improved in the past by thermomechanical treatment, utilization of powder metallurgy provides more controlled microstructure, a homogeneous dispersion of nanosized oxide particles in the metal matrix and tailored properties in terms of strength and radiation resistance. This article is summarizing recent results on preparation, structural, and mechanical investigation of oxide dispersed strengthened steel (ODS). Two commercial steel powders, austenitic 17Cr12Ni2.5Mo2.3Si0.1C and martensitic Fe16Cr2Ni0.2C powders have been used as starting materials. Nanosized yttria dispersed martensitic and austenitic sintered steel samples have been realized by powder metallurgical methods. An efficient dispersion of nano-oxides in ODS steels was achieved by employing high efficient attrition milling. A combined wet and dry milling process of fine ceramic and steel particles is proposed. Spark Plasma Sintering (SPS) was applied to realize nanostructured steel compacts. Grains with 100 nm mean size have been observed by SEM in sintered austenitic ODS. In comparison, the sintered martensitic dry milled and martensitic dry and combined milled ODS microstructure consisted of grain size with 100–300 nm in each case. A brittle behavior is shown in all of the cases. The martensitic ODS is two times harder than the austenitic ODS. The bending strength high as 1806.7 MPa was found for the martensitic ODS, whereas 1210.8 MPa was determined for the austenitic ODS. The combined milling assured higher strength and hardness compared to dry milling.     

微量Sc和Zr对Al—Az—Mg合金组织与性能的影响

采用铸锭冶金法制备了Al-6.2Zn-2.0Mg-0.25Zr和Al-6.2Zn-2.0Mg合金,测试不同处理态的拉伸力学性能。利用金相显微镜和透射电子显微镜研究其不同处理态的显微组织,结果表明：添加微量Sc和Zr可明显细化合金的铸态晶粒,并显著提高Al-Zn-Mg合金的力学性能,其作用机理主要为Al3(Sc,Zr)造成的细晶强化,亚结构强化和弥散强化。     

Joint properties of friction welded 6061 aluminum alloy/YSZ–alumina composite at low rotational speed

In this study, a ceramic composite of alumina–yttria stabilized zirconia (YSZ) was friction welded to 6061 aluminum alloy. Alumina rods containing 25 wt.% YSZ were formed using slip casting and subsequently sintered at 1600 °C to form a solid body. The 6061 aluminum alloy sample was cut and polished, and then subjected to friction welding experiments. Both rods were 16 mm in diameter. The results of this study showed that the alumina–25 wt.% YSZ composite was able to be friction welded to 6061 aluminum alloy at a lower rotational speed of 630 rpm compared with high rotational speeds. The friction force was maintained at 5 KN for a frictional time of 30 s. Optical Microscopy (OM) and Field Emission Scanning Electron Microscope (FESEM) were used to analyze the microstructure of the products, particularly at the interface of the joints. The joints were also examined with EDX line and area (energy dispersive X-ray) in order to determine the phases formed during the low speed welding. The mechanical properties including bending strength and Vickers microhardness were measured. The experimental results indicated that the mechanical strength of friction welded alumina–25 wt.% YSZ composite/6061 aluminum alloy components were obviously affected by joining in the low rotational speed (630 rpm), having higher strength as compared to higher rotational speed.     

Effect of carbon nanotube (CNT) content on the mechanical properties of CNT-reinforced aluminium composites

The interest in carbon nanotubes (CNTs) as reinforcements for aluminium (Al) has been growing considerably. Efforts have been largely focused on investigating their contribution to the enhancement of the mechanical performance of the composites. The uniform dispersion of CNTs in the Al matrix has been identified as being critical to the pursuit of enhanced properties. Ball milling as a mechanical dispersion technique has proved its potential. In this work, we use ball milling to disperse up to 5 wt.% CNT in an Al matrix. The effect of CNT content on the mechanical properties of the composites was investigated. Cold compaction and hot extrusion were used to consolidate the ball-milled Al–CNT mixtures. Enhancements of up to 50% in tensile strength and 23% in stiffness compared to pure aluminium were observed. Some carbide formation was observed in the composite containing 5 wt.% CNT. In spite of the observed overall reinforcing effect, the large aspect ratio CNTs used in the present study were difficult to disperse at CNT wt.% greater than 2, and thus the expected improvements in mechanical properties with increase in CNT weight content were not fully realized.     

Effect of Zn concentration on the microstructures and mechanical properties of extruded Mg–7Y–4Gd–0.4Zr alloys

Microstructures and mechanical properties of the Mg–7Y–4Gd–xZn–0.4Zr (x = 0.5, 1.5, 3, and 5 wt.%) alloys in the as-cast, as-extruded, and peak-aged conditions have been investigated by using optical microscopy, scanning electron microscope, X-ray diffraction, and transmission electron microscopy. It is found that the peak-aged Mg–7Y–4Gd–1.5Zn–0.4Zr alloys have the highest strength after aging at 220 °C. The highest ultimate tensile strength and yield tensile strength are 418 and 320 MPa, respectively. The addition of 1.5 wt.% Zn to the based alloys results in a greater aging effect and better mechanical properties at both room and elevated temperatures. The improved mechanical properties are mainly ascribed to both a fine β′ phase and a long periodic stacking-ordered structure, which coexist together in the peak-aged alloys.     

Effects of calcium on the microstructures and tensile properties of Mg-5Li-3Al alloys

The as-cast Mg-5Li-3Al-xCa (x = 0, 0.5, 1, 1.5 wt.%) was prepared with vacuum induction melting furnace, then processed by hot extrusion. The microstructures and tensile properties were investigated. The results show that the grains of as-cast alloys were refined gradually with the increase of Ca content from 0.5 wt.% to 1 wt.%, while the Ca content increases to 1.5 wt.%, the grain size increases. The microstructures of investigated alloys were further refined after hot extrusion. Both as-cast and as-extruded Mg-5Li-3Al-0.5Ca alloys have the highest mechanical properties, which is mainly attributed to the grain refinement caused by the addition of Ca and the formation of strengthening phase, Al₄Ca. When the addition of Ca is up to 1-1.5 wt.%, the tensile properties of alloys are worsened due to the excessive (Mg, Al)₂Ca eutectic phase forming at grain boundary.