Microstructure and mechanical properties of laser metal deposited AlSi10Mg alloys

Thin-walled specimens with more than 150 layers were deposited by laser metal deposition without cracks and concaving deformation. The microstructure in each layer could be divided into three zones according to the morphology. The homogeneity deteriorated with the rising of the input. The tensile strength dropped 29.7% when the porosity increased from 0.53% to 1.88%. Controlling the oxygen under 0.5% and optimising the heat input, the as-built tensile strength reached 360?MPa. The fracture elongation was enhanced from 3.9% to 12.7% when the heat input was increased from 480 to 1200?W. The decrease of the secondary dendrite arm spacing and the change of fracture mechanism is the main reason leading to the strengthening of the mechanical properties.     

Microstructure and mechanical properties of FexCoCrNiMn high-entropy alloys

The microstructure and tensile properties of Fe_xCoCrNiMn high-entropy alloys (HEAs) were investigated. It was found that the Fe_xCoCrNiMn HEA has a single face-centered cubic (fcc) structure in a wide range of Fe content. Further increasing the Fe content endowed the Fe_xCoCrNiMn alloys with an fcc/body-centered cubic (bcc) dual-phase structure. The yield strength of the Fe_xCoCrNiMn HEAs slightly decreased with the increase of Fe content. An excellent combination of strength and ductility was achieved in the Fe_xCoCrNiMn HEA with higher Fe content, which can be attributed to the outstanding deformation coordination capability of the fcc/bcc dual phase structure.     

Microstructure and mechanical properties of 12 wt.% Cr ferritic stainless steel with Ti and Nb dual stabilization

TCS stainless steel is a 12 wt.% Cr ferritic stainless steel with 0.040 wt.% Ti and 0.096 wt.% Nb dual stabilization. This paper investigated the microstructures and mechanical properties of TCS stainless steel heated at 600–1300 °C for 10 min and followed water quenching. Results show the increasing of both tensile strength and hardness meanwhile the ductility and toughness have experienced the decreasing due to formation of martensitic phase and grain coarsening. In the unheated and heated TCS stainless steel, there are mainly two kinds of particles: Ti-rich particles in size of 2–5 μm; Nb-rich particles in size of 20–50 nm.     

Microstructure and mechanical properties of hot rolled TiNbSn alloys

Titanium alloys with lower elastic modulus and free from toxic elements such as Al and V have been studied for biomedical matters. Ti–Nb–Sn alloys showed up as presenting great potential for the aforementioned purpose. The current study got Ti–35Nb-XSn alloys (x = 2.5; 5.0; 7.5) by applying the following techniques: arc melting, homogenizing and cooling in furnace, homogenizing and water quenched, hot rolling and water quenched. According to each step of the study, the microstructures were featured by means of optical microscopy, by applying a scanning electron microscopy (SEM) analysis as well as X-ray diffraction. The mechanical properties were gotten by means of: Vickers microhardness, tensile and ultrasonic tests. Their ratio between tensile strength and elastic modulus as well as the ductility were compared to other biomedical alloys already available in the literature. The mechanical behavior of the Ti–Nb alloys directly depends on the Sn rates that constitutes the phases as well as on the thermomechanical background to which the alloy was submitted to. The hot rolled Ti–35Nb–2.5Sn alloy showed high ratio between strength and elastic modulus as well as high ductility, just as high as those of some cold rolled Ti alloys.     

Microstructure and mechanical properties of rapidly quenched L20 and L20+L12 alloys in Ni-Al-Fe and Ni-Al-Co systems

Ductile L2₀-type wires and+L1₂-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. _y, _f and _p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in _y and _f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.     

石墨烯增强镁合金塑性加工的组织和力学性能

为获得优异力学性能的复合材料,选用石墨烯作为增强体.本文采用粉末冶金方法,经高能球磨法、冷压、烧结、热压和热挤压制备了AZ31镁合金及石墨烯(GNPs)增强AZ31镁基复合材料棒状试样,通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)和室温拉伸、压缩表征了该材料的组织和力学性能.结果表明:制备的复合材料及基体中生成了Mg_(17)Al_(12)和MgO,加入GNPs后复合材料的屈服强度与维氏硬度都优于基体材料;加入GNPs质量分数为0.5%和1.0%的GNPs复合材料分别比基体屈服强度增加13.2%和14.2%(258和259 MPa),显微维氏硬度分别增加11.4%和14.3%(78和80 HV),主要的强化机制为载荷转移强化、奥罗万强化、热错配强化,但材料的拉伸延伸率分别降低到3.9%和4.3%,比基体分别降低了38%和32%,材料的致密度分别为99.6%、98.5%、97.8%,随着GNPs的增加,致密度降低;GNPs的加入未改变材料的断裂方式,材料的断裂方式均主要为脆性断裂;GNPs的添加使复合材料的基面{0002}织构弱化,从而降低材料的屈服不对称性.     

Microstructure and mechanical properties of rapidly solidified Al-Si-Fe-X base alloys

The effects of Ti and V additions on microstructure and mechanical properties of rapidly solidified Al-20w/oSi-5w/oFe alloy were investigated, respectively. The hypereutectic Al-Si-Fe base alloys were gas-atomized and hot-extruded to make the consolidated bars. The addition of 2w/oTi increased wear resistance and mechanical properties such as tensile strength, hardness and elongation. Based on TEM analyses, it can be concluded that the improved properties in the Al-Si-Fe alloys containing Ti were caused by the formation of DO₂₂-(Al,Si)₃ Ti phase finely dispersed in the matrix. On the contrary, V addition was less effective than Ti, in that V could not decompose as the expected Al₁₀V phase with a large v/o of precipitates; V was mostly solid-solutionized in the other unknown phase.     

Study of the in vitro corrosion behavior and biocompatibility of Zr-2.5Nb and Zr-1.5Nb-1Ta (at%) crystalline alloys

The in vitro corrosion behavior and biocompatibility of two Zr alloys, Zr-2.5Nb, employed for the manufacture of CANDU reactor pressure tubes, and Zr-1.5Nb-1Ta (at%), for use as implant materials have been assessed and compared with those of Grade 2 Ti, which is known to be a highly compatible metallic biomaterial. The in vitro corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements, as a function of exposure time to an artificial physiological environment (Ringer’s solution). Open circuit potential values indicated that both the Zr alloys and Grade 2 Ti undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Zr-1.5Nb-1Ta alloy and that this oxide has better corrosion protection characteristics than the ones formed on Grade 2 Ti or on the Zr-2.5Nb alloy. EIS study showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film presents on the metals surface, improving their resistance with exposure time, presenting the highest values to the Zr-1.5Nb-1Ta alloy. For the biocompatibility analysis human osteosarcoma cell line (Saos-2) and human primary bone marrow stromal cells (BMSC) were used. Biocompatibility tests showed that Saos-2 cells grow rapidly, independently of the surface, due to reduced dependency from matrix deposition and microenvironment recognition. BMSC instead display a reduced proliferation, possibly caused by a reduced crosstalk with the metal surface microenvironment. However, once the substrate has been colonized, BMSC seem to respond properly to osteoinduction stimuli, thus supporting a substantial equivalence in the biocompatibility among the Zr alloys and Grade 2 titanium. In summary, high in vitro corrosion resistance together with satisfactory biocompatibility make the Zr-2.5Nb and Zr-1.5Nb-1Ta crystalline alloys promising biomaterials for surgical implants.     

激光熔凝处理对Zr-1Nb核燃料包壳组织和性能的影响

为了提高核燃料包壳Zr-1Nb合金的抗高温腐蚀性能,采用激光熔凝+真空退火热处理工艺对其进行表面处理。借助扫描电子显微镜(SEM)、X射线衍射(XRD)、拉曼等检测手段对锆管组织、成分及物相结构进行分析,使用探针式表面轮廓仪、显微硬度计和高压反应釜等仪器表征锆合金的粗糙度、硬度和耐蚀性。结果表明:经激光熔凝处理的锆管表面平整度提高;激光熔凝层物相主要由α-Zr和少量的m-ZrO2组成,且后续真空退火热处理没有改变锆合金的相组成;较高功率条件下进行激光熔凝显著降低锆管的高温耐蚀性能,而在较低功率进行激光熔凝工艺且辅助后续热处理的条件下,可以显著提高锆管的高温耐蚀性能;经激光熔凝处理后锆合金的显微硬度升高50~80HV0.1,热处理后硬度相应减小,但仍高于原始样品。     

Microstructure and mechanical properties of Fe3Al alloys with chromium

Alloys based on Fe₃Al have an equilibrium DO₃ structure at low temperatures and transform to a B2 structure above about 550°C. The influence of different rates of quenching from the B2 region to room temperature and of subsequent heat treatments on the microstructure and mechanical properties of powder metallurgy (P/M) alloys with two different chromium contents have been examined. Optimizing the processing to maximize the amount of B2 order, without eliminating dislocations that enhance both strength and ductility, yields room-temperature ductility approaching 20%, although the fracture mode is primarily brittle cleavage. The B2 structure generally has lower flow stress than the DO₃ structure because of its lower strain-hardening rate, although B2 order actually has higher yield strength when the structure is free of dislocations. Increasing the chromium content from 2% to 5% has little effect on ductility, although the 2% Cr alloys generally have higher yield strengths and larger order parameters.     

Microstructure and mechanical properties of two-phase Fe30Ni20Mn20Al30: part II mechanical properties

This paper describes the mechanical properties of B2/L2₁ two-phase Fe₃₀Ni₂₀Mn₂₀Al₃₀ (at.%) in both the as-cast condition and after a 72 h anneal at 823 K. The temperature dependence of the compressive strength of Fe₃₀Ni₂₀Mn₂₀Al₃₀ showed three distinct regions: (1) brittle fracture at low temperature, (2) plastic flow with a rapid decline in yield strength from 1500 to 250 MPa from the brittle-to-ductile transition temperature (BDTT) to 873 K, and (3) a slight decrease in yield strength to ~150 MPa from 873 to 1073 K. Interestingly, the BDTT (573 K) exhibited by the coarser microstructure present in 72 h annealed material was lower than that of the as-cast alloy (623 K). Using both differential scanning calorimetry and in situ heating in a transmission electron microscope, an L2₁-to-B2 transition was found at 750 ± 25 K. A mixture of intergranular fracture and transgranular cleavage was observed after room temperature compression while only cleavage was found at 673 K. All the specimens deformed extensively without fracture when tested at temperatures higher than 673 K. The strain rate had little effect on the strength at 573 K and a moderate effect at 873 K with a strain-rate sensitivity exponent value of 0.1.     

Structure and mechanical properties of as-cast Ti–5Nb–xCr alloys

As-cast Ti–5Nb and a series of Ti–5Nb–xCr with Cr content ranging from 1 to 13 mass% prepared by using a commercial arc-melting vacuum-pressure casting system were investigated. Commercially pure titanium (c.p. Ti) was used as a control. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys obviously had different structures and mechanical properties with the addition of various amounts of Cr. When 1 mass% Cr was added, the structure was comprised mainly of the α′ phase, which was also found in Ti–5Nb. With the addition of 3 mass% Cr, α′ and α′′ phases were appeared. When the Cr content was increased to 5 mass% or greater, the β phase was completely retained. Moreover, the ω phase was detected in the Ti–5Nb–5Cr and Ti–5Nb–7Cr alloys. The largest quantity of ω phase and the highest bending modulus were found in the Ti–5Nb–5Cr alloy, while the Ti–5Nb–9Cr alloy had the lowest bending modulus. Moreover, the high strength/modulus ratios of the Ti–5Nb–3Cr (22.5) and Ti–5Nb–9Cr (21.3) alloys demonstrate its advantage for use as implant materials. Also, these two alloys exhibited the better elastic recovery angles of 28.3° in Ti–5Nb–3Cr and 22.2° in Ti–5Nb–9Cr. In the current search for better implant materials, α′ + α′′ phase Ti–5Nb–3Cr and β phase Ti–5Nb–9Cr alloys with low modulus, ductile property, excellent elastic recovery capability and reasonably high-strength seem to be the most feasible alloy for orthopedic and dental applications if some other necessary properties are obtained.     

Structure and mechanical properties of as-cast Ti–5Nb–xFe alloys

In this study, as-cast Ti–5Nb and a series of Ti–5Nb–xFe alloys were investigated and compared with commercially pure titanium (c.p. Ti) in order to determine their structure and mechanical properties. The series of Ti–5Nb–xFe alloys contained an iron content ranging from 1 to 5 mass% and were prepared by using a commercial arc-melting vacuum-pressure casting system. Additionally, X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer, and three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys possessed a range of different structures and mechanical properties dependent upon the various additions of Fe. With an addition of 1 mass% Fe, retention of the metastable β phase began. However, when 4 mass% Fe or greater was added, the β phase was entirely retained with a bcc crystal structure. Moreover, the ω phase was only detected in the Ti–5Nb–2Fe, Ti–5Nb–3Fe and Ti–5Nb–4Fe alloys. The largest quantity of ω phase and the highest bending modulus were found in the Ti–5Nb–3Fe alloy. The Ti–5Nb–2Fe alloy had the lowest bending modulus, which was lower than that of c.p. Ti by 20%. This alloy exhibited the highest bending strength/modulus ratio of 26.7, which was higher than that of c.p. Ti by 214%, and of the Ti–5Nb alloy (14.4 ) by 85%. Additionally, the elastically recoverable angles of the ductile Ti–5Nb–1Fe (19.9°) and Ti–5Nb–5Fe (29.5°) alloys were greater than that of c.p. Ti (2.7°) by as much as 637% and 993%, respectively. Furthermore, the preliminary cell culturing results revealed that the Ti–5Nb–xFe alloys were not only biocompatible, but also supported cell attachment.     

Microstructure and mechanical properties of RSP/M Al-Fe-V-Si and Al-Fe-Ce alloys

Two aluminium alloys with nominal compositions of Al-8Fe-4Ce and Al-8Fe-1V-2Si (all compositions in wt%) were rapidly solidified by ultrasonic gas atomization. The atomized powders with an average particle size (d₅₀) of 30 m were vacuum hot pressed and subsequently hot extruded. The P/M extrusion exhibited similar microstructure and elevated temperature tensile properties. The tensile and stress rupture samples of both the alloys exhibited ductile dimple failure. However, the Al-Fe-V-Si extrusion samples exhibited significantly better creep and stress rupture properties. The Al-Fe-Ce alloy was found to be more susceptible to cavitation at elevated temperatures which resulted in poor stress rupture properties.     

Microstructure and mechanical properties of modified and non-modified stir-cast Al-Si hypoeutectic alloys

The microstructure and mechanical properties of modified and non-modified stir-cast commercial aluminium alloys A-S7G03 and A-S4G have been investigated. Stir casting of these alloys resulted in spherical and/or rosette shape primary -phase, and the eutectic silicon was broken into miniature needle morphology. This stir-cast structure slightly improved the mechanical properties in comparison to those of conventionally cast alloys, however the fracture of the stir-cast alloys revealed intergranular brittle fracture. The addition of 0.02% strontium, in the form of Al-5 mass% Sr master alloy, during stir casting modified the eutectic silicon into a very fine spheroidal morphology, while the -phase particle showed the same morphology as the stir-cast alloys. This novel structure resulted in significant improvement of mechanical properties. The elongation of the modified stir-cast alloys was five times greater than that of the non-modified one. A transgranular mode of fracture was observed for the modified stircast alloys, moreover smooth ripple and dimple patterns were observed reflecting the high ductility of the modified stir-cast alloys.     

Effects of Zn / Y ratio on microstructure and mechanical properties of Mg-Zn-Y alloys

Microstructures and mechanical properties of Mg-Zn-Y alloys containing icosahedral phase (I-phase) as a secondary solidification phase have been investigated in the composition range where the total solute content (Zn and Y) is less than 10 wt.%. The optimum Zn / Y ratio for the formation of two-phase microstructure consisting of α-Mg and I-phase is 5∼7. The strength increases with increasing total solute content (Zn and Y), i.e. with increasing volume fraction of I-phase. In particular, the alloys containing I-phase exhibit high elongation to failure, > 25%, which is ascribed to the low interfacial energy between the I-phase particle and surrounding α-Mg crystalline matrix.     

Structure and mechanical properties of internally hydrided Mg-IIIa transition metal alloys

Magnesium alloys containing III_a transition metals, such as Sc, Y and Ho, respectively, were hydrogenated at 773 K and examined for microstructure, X-ray diffraction pattern, micro-Vickers hardness, and tensile properties at room and high temperatures. Results obtained are as follows:

1. The alloys, respectively, have been internally hydrided and have precipitated hydrides of the III_a transition metals as small flake-like particles in the matrix and at grain boundaries, as well as twin boundaries.
2. The dispersed hydride particles do not necessarily contribute to further hardening of the alloys at room temperature and up to near 673 K.
3. However, the dispersed particles are very stable and seem to improve mechanical properties of the alloys above 673 K.
4. Presumed relationships of crystallographic coincidence between the matrix and hydrides have been obtained.

     

Microstructure and mechanical properties of as-cast Mg-4Zn-0.5Zr-0.2Cu-0.2Ce alloy

In this study, an approach is proposed to improve the microstructure and mechanical properties of Mg-4Zn-0.5Zr alloy by combining trace Cu and rare earth Ce addition. The results showed that Cu and Ce additions led to obvious grain refinement and the formation of Mg-Zn-Cu and Mg-Zn-Ce phases. The Mg-Zn-Ce phase was identified to have an orthorhombic structure. The length of the [0001]_α rods in the Cu-containing alloys remarkably decreased. The yield strength increased slightly after Cu and Ce co-addition, which was attributed to grain refinement and precipitation strengthening. The coarse Mg-Zn-Ce phase distributed at the grain boundaries would reduce the ductility by promoting crack propagation during tensile processes.     

Use of Ti in hard metal alloys – Part II: mechanical properties

WC‐Co hard metal is a material of high hardness, high compressive strength and wear resistance while maintaining good toughness and thermal stability. Samples of nanosized WC powders with 10 wt% Co, WC‐10 wt% Ti, WC‐9 wt% Ti‐1 wt% Co were cold pressed at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar. The characterization of the sintered materials was performed by the measurements of densification, HV30 hardness, fracture toughness and compression strength. The results showed that it is possible to process a hard metal through a Powder Metallurgical conventional route from nanoscaled WC grains, using Ti (or a Ti‐Co mixture) as a binder phase, with good mechanical properties.     

Influence of Nb addition on microstructural evolution and compression mechanical properties of Ti-Zr alloys

In order to expand the application horizon of Ti-Zr based alloys,the influence of Nb content on phase composition,microstructural evolution and biomechanical properties is systematically studied.The phase and microstructural characterization of the as-cast alloys is carried out by X-ray diffraction,optical microscopy and transmission electron microscopy.The results reveal that Nb-containing Ti-Zr alloys transformed from single a phase→α+α+β phase single β phase double β phases with increasing Nb content.In the case of β-type alloys,the addition of Nb improves the bonding energy between atoms,reduces the grain size,increases the elastic modulus,improves the yield strength and renders superior work-hardening behavior.Moreover,the current study provides mechanistic insights into microstructural evolution and strengthening of Nb-containing Ti-Zr alloys with increasing Nb content.Herein,the addition of 5 at.% Nb resulted in an abnormal work hardening during compression deformation under the synergistic influence of stress-induced martensite transformation of β phase and stress-induced twinning of α phase.Moreover,the biomechanical properties are evaluated to demonstrate the potential of Nb-containing Ti-Zr alloys in biological applications.