Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation

Microstructure and mechanical properties of Ni3Al intermetallics prepared by directional solidification electromagnetic cold crucible technique

The present work focused on the Ni_3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidified Ni-25 Al alloy. Ni_3 Al intermetallics were prepared at different withdrawal rates by directional solidification(DS) in an electromagnetic cold crucible directional solidification furnace. The DS samples contain Ni_3 Al and Ni Al phases. The primary dendritic spacing(λ) decreases with the increasing of withdrawal rate(V), and the volume fraction of Ni Al phase increases as the withdrawal rate increases. Results of tensile tests show that ductility of DS samples is enhanced with a decrease in the withdrawal rate.

Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys

This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. With increasing boron content in the as-cast alloys, there is an increase in the fraction of the γ′/γ eutectic and block borides precipitate around the γ′/γ eutectic. At a high boron content of 0.03wt%, there is precipitation of lamellar borides. Upon heat treatment, fine block borides tend to precipitate at grain boundaries with increasing boron content. Overall, the rupture life of the directionally solidified superalloy is significantly improved with the addition of nominal content of boron. However, the rupture life decreases when the boron content exceeds 0.03wt%.

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.

A study of microstructure and properties of cast Fe-10Cr-1.5B alloy

In the present study, the microstructure and mechanical properties of cast Fe-10Cr-1.5B（FCB） alloy after different heat treatments were studied. The results showed that the as-cast microstructure of FCB alloy consists of α-Fe, M（M=Cr, Fe, Mn）2（B, C） and M（M=Cr, Fe, Mn）7（C, B）3 type borocarbides, and small amounts of pearlite and austenite. After oil quenching treatment, metal matrix transformed into the martensite from the mixture of martensite, pearlite and austenite. There are many M（M=Cr,Fe,Mn）23（C,B）6 type borocarbide precipitates in the metal matrix, and eutectic borocarbide appears with an apparent disconnection and isolated phenomenon. When the quenching temperature reaches 1,050℃, the hardness of FCB alloy is the highest, but the change of quenching temperature has no obvious effect on impact toughness of FCB alloy. After tempering, the eutectic microstructure of FCB alloy appears with a ＂two links＂ trend. With the increase of tempering temperature, the hardness of FCB alloy decreases gradually and impact toughness increases gradually. Cast FCB alloy oil-quenched from 1,050℃ and tempered from 200℃ has excellent combined properties; its hardness and impact toughness are 61.5 HRC and 8.8 J·cm^-2 respectively.

Solidification Properties of CaO-SiO_2-TiO_2 Based Mold Fluxes

In continuous casting of peritectic steel grades sensitive to longitudinal cracking, the solidification properties of mold fluxes play an important role in keeping smooth running of continuous casting process and achieving high surface quality of casting strands. To reduce fluorine pollution in molten slag, types of CaO-SiO2-TiO2 （CTS） based mold fluxes were investigated. The solidification and crystallization properties, including viscosity η at 1 573 K, break temperature Tbr, crystallization ratio Rc and solidification mineragraphy were measured, which were compared with those of CaO-SiO2-CaF2 based mold fluxes. The experiments show that there are unstable viscosity-high tem- perature properties and high Tbr in part of CTS slag system, which are bad for lubrication between liquid flux film and strand. And when temperature is below Tbr, the viscosities change slowly during cooling in some part of this slag system, which imply that liquid mold fluxes solidify slowly and it is easy to cause surface longitudinal cracks on strand. Major mineragraphy of the CaO-SiO2-TiO2 based mold fluxes are CaO · TiO2 or CaO · TiO2 and CaO · SiO2 · TiO2. TiN and Ti（C,N） can be formed in mold fluxes bearing high TiO2 during the continuous casting.

Influence of high pressure during solidification on the microstructure and strength of Mg-Zn-Y alloys

The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction（XRD） and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg_3YZn_6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg_3Y_2Zn_3 and Mg_3YZn_6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZ n and Mg12 YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.

Nucleation undercooling, solidification structures and magnetic properties of Nd_9Fe_(85–x)Ti_4C_2B_x (x=10–15) magnetic alloys

Nd_9Fe_（85–x）Ti_4C_2B_x（x=10–15） magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, the liquidus temperatures TL of the alloys decreased from 1498.5 to 1472.5 K; the solidus temperatures TS of them increased from 1353.2 to 1358.3 K; and the nucleation undercooling of the alloy melts cooled at the rate of 40 K/min decreased from 122.8 to 95.9 K, resulting in the solidification structures consisting of Nd_2Fe_（14）B, Fe_3B, α-Fe, Nd1.1Fe4B4 and TiC nanocrystallines. Furthermore, the Nd_9Fe_（85–x）Ti_4C_2B_x（x=11, 13, 15） bulk alloys in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and their solidification characteristics and solidification structures under sub-rapidly cooling rate were investigated. The results showed that partially amorphous structures were obtained in the as-cast bulk alloys and the amount of amorphous decreased with the increase of the B content. By annealing the as-cast bulk alloys at 923 K for 10 min, the nanocomposite microstructures composed with Nd_2Fe_（14）B, Fe_3B and α-Fe nanocrystallines, which showed a single-phase hard magnetic behavior and enhanced magnetic properties, were achieved.

Microstructure, Microsegregation, and Mechanical Properties of Directional Solidified Mg–3.0Nd–1.5Gd Alloy

The microstructure, microsegregation, and mechanical properties of directional solidified Mg–3.0Nd–1.5Gd ternary alloys were experimentally studied. Experimental results showed that the solidification microstructure was composed of dendrite primary a（Mg） phase and interdendritic a（Mg） · Mg12（Nd, Gd） eutectic and Mg5 Gd phase. The primary dendrite arm spacing k1 and secondary dendrite arm spacing k2 were found to be depended on the cooling rate R in the form k1= 8.0415 9 10-6R-0.279 and k2= 6.8883 9 10-6R-0.205, respectively, under the constant temperature gradient of40 K/mm and in the region of cooling rates from 0.4 to 4 K/s. The concentration profiles of Nd and Gd elements calculated by Scheil model were found to be deviated from the ones measured by EPMA to varying degrees, due to ignorance of the back diffusion of the solutes Nd and Gd within a（Mg） matrix. And microsegregation of Gd depended more on the growth rate, compared with Nd microsegregation. The directionally solidified experimental alloy exhibited higher strength than the non-directionally solidified alloy, and the tensile strength of the directionally solidified experimental alloy was improved,while the corresponding elongation decreased with the increase of growth rate.