Effect of strontium on microstructure, mechanical, and biological responses of Mg–Al–Zn–Sr alloys

Enhancement of microwave absorption properties of SrxFe12-yPr0.4o19-θ (x=0.6–1.3, y=0∼0.4) by tuning the calcination temperatures

Microstructural and mechanical characterization of injection molded 718 superalloy powders

Quantitative phase analysis of Ti-3Al-5Mo-4.5 V dual phase titanium alloy by XRD whole pattern fitting method

Microstructural and fractographic observations were systematically done on Fe-30Mn(6-x)Si-xAl (x=0, 1, 2 and 4 mass %) alloys. Optical and transmission electron microscopic observations and X-ray diffractions revealed that the deformation mode continuously shifts from the stress induced fcc/hcp martensitic transformation to the mechanical twinning of the fcc austenite as the Al content increases. It was also clarified by the scanning electron microscopic observations that the microstructural change depending on the Al content is accompanied by the change in the fracture mode from the quasi-cleavage fracture to the ductile fracture. INTRODUCTION Fe-Mn-Si-based shape memory alloys (SMAs) exhibit the shape memory effect (SME) associated with fcc (γ-austenite) / hcp (e-martensite) martensitic transformation [1]. A recoverable strain obtained in a typical Fe-Mn-Si SMA: e. g. Fe-30Mn-6Si (hereinafter compositions are shown in mass%), was reported about 2% in the solution treated condition [2]. This value can be increased to about 4% by so-called the training treatment [3, 4] and fine dispersion of precipitates such as NbC carbides [5-7], etc. One drawback of the alloy was its poor ductility of about 30%. In contrast to this, it was recently reported that the Fe-30Mn-3Si-3Al TWIP (Twinning Induced Plasticity) steel exhibits the ultra-high ductility as much as about 90% [8], but this alloy shows no significant SME. The composition of the Fe-30Mn-3Si-3Al TWIP steel is such that a part of Si in the Fe30Mn-6Si SMA is replaced by Al. In order to systematically investigate the effect of the Al content on the SME and TWIP effect, the present authors prepared four kinds of FeMn-Si-Al alloys by gradually varying the amount of Al substituting Si: i. e. Fe-30Mn(6-x)Si-xAl (x=0, 1, 2 and 4). The following two conclusions were drawn as a result [9]: i) the alloys with x=0 and 1 exhibited similar SME, but no recognizable SME was observed for the alloys with x>2, ii) the ductility linearly increased with increasing the amount of Al. The above-mentioned changing tendencies may originate from the continuous change in the deformation mode from the stress-induced γ → e martensitic transformation to the mechanical γ twinning. However, there has been no systematic study on the effect of the Al content on the deformation and fracture modes between the SMA and the TWIP. In the present paper, microstructural observations using optical microscopy (OPM) and transmission electron microscopy (TEM), phase identification using X-ray diffraction (XRD) and the fractographic observations using scanning electron microscopy (SEM) were carried out to clarify the effect of the Al content on the deformation mode and the corresponding fracture mode of the alloys. EXPERIMENTAL In this paper, hereafter the Fe-Mn-(6-x)Si-xAl (x=0, 1, 2 and 4) alloys are referred to as Al-0,Al-1,Al-2,Al-3 using mass % of Al. The specimens were prepared by vacuum induction melting. After hot forging and rolling at 1270K, the specimens were subjected to solution treatment at 1270K for 3h followed by water quenching. The OPM observations were performed on the samples, which were mechanically and electrolytically polished to obtain smooth surfaces and then extended by about 3%, using a differential interference microscope. The phase constitutions and internal microstructures in the deformed specimens were investigated with a RINT 2500 X-ray diffractometer and with a JEOL 2000FX II transmission electron microscope, respectively. The specimens for TEM observation were carefully prepared to avoid the formation of stress-induced martensite and reverse transformation on heating, using a chemical polishing solution of hydrogen peroxide and hydrofluoric acid mixed in the ratio of 10: 1. The specimens were finally subjected to electropolishing using acetic acid and perchloric acid mixed in the ratio of 20:1 at room temperature, to obtain the TEM foils. Fracture surfaces were examined on the specimens fractured at room temperature with a Hitachi S-3100 scanning electron microscope. RESULTS AND DISCUSSION DEFORMATION BEHAVIOR Figures 1 (a) to (d) show the OPM images observed on the specimens of Al-0 to Al-3, respectively, deformed by tensile strain to 3%. Some grains seen in the figures involves anneal twins. Anneal twin boundaries on {111}γ planes are indicated by arrows in the OPM photos. In each of parent and twin crystals, there are surface striations. It should be noted in Figs. 1(a) to (d) that the width and interval of the striations inside crystals becomes smaller with increase in the Al content. It has been widely accepted that the striations appeared in the Fe-Mn-Si SMAs are formed by the stress-induced γ → e martensitic transformation, while those in the FeMn-Si-Al TWIP steels are due to the mechanical γ twinning. It is inferred from the variation in the microstructures from Figs. 1(a) to (d) that the deformation mode should continuously change from the stress-induced e martensite to the mechanical γ twins, when the Al content is increased from 0 mass % to 3 mass %. Our previous result [9] showing the linear change in the ductility depending on the Al content also supports this speculation. However, it is difficult to distinguish these two deformation products by OPM observations, because both have plate shapes on the {111}γ habit. Figure 1: Deformation microstructures observed by optical microscopy on the specimens of (a) Al-0, (b) Al-1, (c) Al-2, and (d) Al-3. The observations were performed at the tensile strain of about 3%. The phase identification by means of the XRD was, therefore, performed to investigate semi-quantitatively the dependence of the amount of the e phase on the Al content. It was revealed that the intensity of peaks from the e phase relative to that of peaks from the γ phase gradually decreases with increasing the Al content, though not presented here. However, it is impossible to investigate the amount of the mechanical γ twins by the XRD. In order to confirm the existence of the e phase and the γ twins, the electron diffraction pattern analysis using TEM was employed. Figure 2(a) shows the bright field image taken in the Al-0. The plates observed in Fig. 2(a) were identified as the e phase by the corresponding electron diffraction pattern shown in Fig. 2(b). The incident beam is parallel to [011]γ // [21 1 0]e. The diffraction pattern in Fig. 2(b) clearly shows the well known features of the γ → e transformations: i) the S-N orientational relationship between the γ and e crystals, ii) the streaks along γ directions due to small thickness of the e plates. The streaks run in two directions: i. e. and . The (11 1) and (111 ) traces nominal to the corresponding streaks are seen in Fig. 2(a). Figure 2(c) and (d) show an example of the mechanical γ twins (γTM) observation in the Al-3. The zone axes of the diffraction pattern are [011]γ // [011]γTM. A lamella structure consisted of nano-sized twins and the retained austenite is formed in the specimen, being consistent with the previous results in the literature [10]. After a number of careful observations, a very small amount of the e plates were also found even in the Al-3, although it was undetectable in the XRD profile. 200 111 111 MT 200 MT

Effect of microstructure evolution on mechanical property of extruded Mg–12Gd–2Er–1Zn–0.6Zr alloys

In this study, Fe-Ag and Fe-Au composites were fabricated by powder metallurgy using spark plasma sintering. Their microstructures, mechanical properties, and biocorrosion behavior were investigated by using optical microscopy, X-ray diffraction, environment scanning electronic microscopy, compressive test, electrochemical measurements, and immersion tests. Microstructure characterization indicated that the as-sintered iron-based materials obtained much finer grains than that of as-cast pure iron. Phase analysis showed that the Fe-Ag composites were composed of α-Fe and pure Ag phases, and Fe-Au composites consisted of α-Fe and Au phases. Compressive test showed that the improved mechanical strengths were obtained in as-sintered iron-based materials, among which the Fe-5 wt %Ag exhibited the best mechanical properties. The electrochemical and immersion tests revealed that the addition of Ag and Au could increase the corrosion rate of the iron matrix and change the corrosion mode into more uniform one. Based on the results of cytotoxicity evaluation, it was found that all the experimental material extracts performed no significant toxicity on the L-929 cells and EA. hy-926 cells, whereas a considerable inhibition on the proliferation of vascular smooth muscle cells was observed. The hemocompatibility tests showed that the hemolysis of all the experimental materials was within the range of 5%, which is the criteria value of biomaterials with good hemocomaptibility. The amount of platelet adhered on the surface of as-sintered iron-based materials was lower than that of as-cast pure iron, and the morphology of platelets kept smoothly spherical on the surface of all the experimental materials.

La1−x Sr x FeO3 (x = 0.0–1.0) nanoparticles have been synthesized by a sol–gel method. The samples are characterized by thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The La1−x Sr x FeO3 (x = 0.0–1.0) materials have been sintered at 650 °C. Both the structural properties and phase transitions with increasing strontium content in La1−x Sr x FeO3 are presented by analysis of XRD data. Formaldehyde gas-sensing properties of La1−x Sr x FeO3 have been investigated. The experimental results show that the optimum operating temperatures of La1−x Sr x FeO3 varies with Sr content of x. Among all the samples, La0.7Sr0.3FeO3 shows a maximum response to formaldehyde. Finally, the formaldehyde gas-sensing mechanism has been presented.

The effect of strontium on the microstructure and mechanical properties of Mg–6Al–0.3Mn–0.3Ti–1Sn

Preparation of bimodal grain size 7075 aviation aluminum alloys and their corrosion properties

A seam welded Cr-Mo steel pipe elbow that had been used as main steam piping at a thermal power plant was investigated. Creep damages at fine grained heat affected zone of the seam weld, called as type IV damages, were observed. Hook-shaped microcracks surrounded by many polygonal hollows were observed by optical microscopy and scanning electron microscopy. Those polygonal hollows were seemed to form the same hook-shaped lines as microcracks. Fine bainite grains surrounded by coarse carbides and creep cavities were also lined in the same manner as the hollows. From the appearances of the hook, it was inferred that these damages were originated locally at the former austenite grain boundaries.Dense precipitations of carbides (DPCs) were found on extraction replicas by transmission electron microscopy. At the beginning of the usage, there might be high-carbon-content fine bainite grains and DPCs were created in these grains by aging. Because of the similarities in shapes, sizes and distributions, DPCs were regarded as root causes of the hollows and the cracks. Many creep cavities would appear at DPCs and fine bainite grains would easily be isolated. As DPCs line on the former austenite grain boundaries, exfoliated fine bainite grain boundaries would link each other to form a microcrack.In order to suppress type IV damage, it would be effective to avoid the origination of fine bainite with high-carbon-content grains on the former austenite grain boundaries. Adding normalizing twice or more to the heat treatment process for the plate materials before welding is proposed.

The effect of strontium content on the tensile properties of squeeze cast Mg–Al–Sr alloy was investigated. Three strontium contents, 0, 1·5 and 3·0 wt-%, were added to a Mg–6Al alloy (AM60 alloy) which was squeeze cast under an applied pressure of 30 MPa. Tensile test results indicated that the ultimate tensile strength, yield stress and elongation of the squeeze cast Mg–Al–Sr alloy decreased with increasing strontium content. Microstructural analysis indicated that Sr content influenced a number of phases present in the squeeze cast alloys. Also, the grain size of the alloys was observed to decrease with increasing strontium content. It is proposed that an increase in porosity following Sr addition, which appears to offset its grain refinement effect, is responsible for the decrease in tensile properties.

Synthesis and characterization of lead strontium titanate thin films by sol–gel technique

Electron Backscatter Diffraction (EBSD) in Scanning Electron Microscope (SEM) has been one of the most popular tools for characterizing microstructures of materials and in particular alloys made by additive manufacturing (AM) in recent years. This characterization technique can provide abundant microstructural data, including phase distribution, grain size, grain boundary character, crystallographic orientation, and texture. However, it has recently been noticed that there are several challenges in the characterization of AM alloys by EBSD, causing the misunderstanding of material microstructures. This presentation discusses two challenges associated with the grain size determination by EBSD. Grain size is an important parameter used in understanding the relationship between the mechanical property and microstructure of a 3D-printed alloy, and is usually measured by optical microscope (OM) and EBSD. However, a common issue is that the grain size determined by EBSD sometimes is inconsistent with that from OM. Here We measured the grain size from the same areas in a Ti64 sample by OM and EBSD, respectively, and compared the results, in order to correlate two techniques. The result shows that when the grain size is greater than 10um, the data from OM and EBSD can completely match. When the grain size is in the range of 4~10um, there is a significant deviation between the size distributions. For fine grains, e.g. <4um, the EBSD measurement is more reliable. This indicates that OM and EBSD are equivalent for analyzing grains which sizes are bigger than 10um, but EBSD is more suitable for measuring fine grains due to the higher spatial resolution than OM. Further analysis reveals that the accuracy of grain size measurement especially for the fine grains is strongly related to the threshold angle of grain boundary used in the EBSD data process. Step size is another important parameter to determine the grain size. Another usual challenge in the EBSD analysis is how to choose the step size to obtain a high-quality EBSD map with high spatial resolution and high hit rate [1]. As the typical AM alloy has two different microstructural features in terms of grain size, melt pools with large columnar grains and fine-grained regions between the melt pools, researchers like to choose a small step size to map the sample. This is a conventional EBSD strategy used in the characterization of heterogeneous microstructures in materials. However, the recent characterization in Al printed alloys shows that such a strategy doesn’t work well at low magnification even a very small step size is used. Normally, grains in melt pools are visualized and measured well, but the fine grains at the melt pool boundaries are invisible at the low magnification due to the low hit rate. To improve EBSD map quality and grain size measurement at the fine-grained regions, higher magnification with a smaller step size has been used, but this condition limits the size of the mapping area. Compromising the magnification and grain size determination, a new EBSD strategy that includes two steps of mapping AM samples is recommended, firstly scanning a big area to show the domain microstructures of melt pools, and secondly mapping with higher magnification to show the typical fine-grained region in detail.

The effects of HIP processing on microstructure and phase relations in α2-base titanium aluminides

The effects of HIP processing on microstructure and phase relations in α2-base titanium aluminides