Oxidation Behavior of NiAl-30.75Cr-3Mo-0.25Ho Alloy at High Temperatures

The oxidation behavior of NiAl-30.75Cr-3Mo-0.25Ho alloy from 1300 to 1500 K in air atmosphere was investigated. The results reveal that oxidation resistance of the alloy is improved by the addition of Ho. At 1500 K, the oxidation kinetic curve obeys the parabolic law (n≈0.5), whereas the oxidation kinetic curve of the tested alloy follows the cubic relations (n≈0.3～0.4) from 1300 to 1450 K. An activation energy of about 261 kJ·mol-1 was determined for the tested alloy. It is found that a continuous and compact Al2O3 layer has formed on the surface of NiAl-30.75Cr-3Mo-0.25Ho alloy after oxidation 100 h at various tested temperatures. A rich-Ho solution formed on the boundaries of Cr(Mo) phase. Doped little amount of Ho in NiAl-31Cr-3Mo alloy promotes the transformation from θ-Al2O3 phase to α-Al2O3 phase, and decreases the size of Al2O3 and the crack forming in the oxidation scale prolongs the spalling time of the film at high temperature. The volatilizing oxides of Cr, Mo and the reactive element effects (REEs) make the mass gain lower than that of pure NiAl.     

Effect of calcium addition on microstructure,casting fluidity and mechanical properties of Mg-Zn-Ce-Zr magnesium alloy

The influence of Ca addition on the as-cast microstructure, casting fluidity and mechanical properties of the Mg-4.2Zn-1.7Ce-0.5Zr(wt.%) alloy was investigated. The results showed that the as-cast alloys consisted of α-Mg matrix, Ca-contained T-phase and Mg51Zn20 phase. Addition of 0.2 wt.%–0.6 wt.% Ca led to effective grain refinement and enhanced the fluidity of the alloys. When the content of Ca was 0.2 wt.%, the alloy exhibited the finest grain size of 35.9 μm, and the filling length was increased by approximately 55.4% compared with the quaternary alloy. The improvement of the fluidity was attributed to the grain refinement, less energy dissipation and the oxidation resistance of Ce and Ca. With an increase in Ca content, the yield strength increased gradually, whereas the ultimate tensile strength and elongation showed a decreasing tendency. Moreover, the fracture surface mode was quasi-cleavage fracture.     

Grain refinement of AZ31 magnesium alloy by AI-Ti-C-Y master ahoy

Al-Ti-C-Y master alloy was prepared by combining SHS technique and melting-casting method. The microstructure of master alloy and its grain-refining effect on AZ31 alloy were investigated by means of OM, XRD, SEM and EDS. Experimental results indicated that the prepared master alloy consisted of α-Al, TiAl3, TiC and Al3Y phases, and exhibited good grain-refining performance of AZ31 alloy. Morphology of α-Mg changed from coarse dendritic to free equiaxed and the average grain size of α-Mg matrix reduced from the original 580 to 170 μm after adding 1.0 wt.% master alloy. The grain refining efficiency of Al-Ti-C-Y master alloy on AZ31 alloy was mainly attributed to heterogeneous nucleation of TiC particles and grain growth restriction of Al-Y compound or TiC at grain boundaries.     

Study on microstructure and mechanical properties of ZL107 alloy added with yttrium

The effects of Y on the microstructure and mechanical properties of ZL107 alloy were investigated using optical microscope, scanning electron microscope (SEM), Brinell hardometer, and MTS 810-22M tensile testing machine in this paper. The results showed that after Y was added to ZL107 alloy, the size of α-Al dendritie reduced, the acicular eutectic Si became short rod-shaped or granular, and the number and size of the blowholes obviously reduced. The mechanical properties of ZL107 alloy firstly increased and then decreased with Y content increasing. When Y content was 0.1 wt.%, the tensile strength and hardness of the alloy were maximum.     

Surface Oxidation of Al2O3/SiC Nanocomposite： Phase Transformation and Microstructure

The surface oxidation behavior of pressureless sintered Al2O3/SiC nanocomposite was studied from 1000 to 1400 ℃ for more than 10 h in air. Weight gain during the process of heat treatment was measured by TG analysis. Phase transformation and microstructure changes of these specimens due to oxidation were investigated with X-ray diffraction (XRD), SEM and EDX technology. Thermogravimetric analysis show that the weight gain as a result of oxidation of SiC become significant above 1200 ℃. In the range of 1000～1300 ℃, the SiC grits are usually coated with a layer of amorphous silica after oxidation. Above 1300 ℃, the amorphous silica reacted with alumina matrix and formed mullite or crystallized into cristobalite. The rate of oxidation depends on the formation of dense cristobalite film. Large amount of needle-like mullite and alumina crystals are formed on the surface after oxidation at 1400 ℃.     

Preparation and properties of Al-Mn alloy coatings in NaCl-KCl-AlCl3-CeCl3 molten salts

Al-Mn alloy coatings were electrodeposited on an iron substrate from AlCl3-NaCl-KCl molten salts with anhydrous MnCl2 enhanced by the addition of CeCl3. The microstructure and properties of the Al-Mn alloy coatings were investigated, and scanning electron microscopy, X-ray diffraction, and polarization curves were used to determine the composition, surface morphology, phase structure, and corrosion resistance of the obtained deposits. The results showed that the surface coatings were smooth, and that the crystallites were dense and uniform when 0.22 wt.% CeCl3 was added to the molten salt. An amorphous mixture of Al and Al6Mn was obtained. CeCl3 enhanced the corrosion resistance and increased the hardness of the single amorphous phase alloys. The pitting potential of the coating was approximately -1.1239 V, and its hardness was 390 kgf/mm2.     

Effect of Mo on the continuous cooling transformation behavior of Nb-Ti micro-alloyed low carbon steel

The effect of molybdenum on the continuous cooling transformation behavior of the micro-alloyed low carbon steel containing niobium and titanium was investigated by a Gleeble 3800 thermo-mechanical simulator.The phase transformation temperature of the steel at various cooling rates was detected.The microstructure was observed by optical microscope(OM) and scanning electronic microscope(SEM),and its Vickers hardness was tested.Based on these,its dynamic continuous cooling transformation(CCT) diagrams were determined.The results show that the transformation temperature from deformed austenite to acicular ferrite(AF) is decreased when Mo is added,and the formation of pro-eutectoid ferrite(F) and pearlite(P) is either inhabited or postponed.Mo can also enlarge the range of the cooling rate in forming AF,and refine the microstructure effectively.     

Influence of strontium and lanthanum simultaneous addition on microstructure and mechanical properties of the secondary Al-Si-Cu-Fe alloy

In this paper, modification agents with different contents of Sr and La elements were added into Al-Si-Cu-Fe alloy and the effect on refinement of secondary phases and α-Al grain was investigated by optical microscopy, scanning electronic microscopy and X-ray diffractometry. Tensile testing was carried out to characterize the strength of the alloys. The XRD result indicated that Fe_9LaSi_4 and SrSi_2 phases were formed after Sr and La elements were added in the alloys simultaneously. With the help of metallographic analysis techniques, the length of needle-like phases, mainly composed of eutectic Si and β-Fe, was quantified. And the secondary dendrite arm spacing(SDAS) of α-Al grain was also evaluated. The quantification results indicated that the modification agents with different contents of Sr and La elements showed varied refinement effects on the mean length of needle-like phases and SDAS value. When the addition amount increased, the length of needle-like phase and SDAS value were decreased. The minimum mean length of needle-like phases(Sr/La=1:1) and the SDAS value(Sr/La=1:5) were obtained by setting the addition amount of the modification agent at 0.12 wt.%. The yield strength of the alloy was related to the mean SDAS value, whilst the ultimate tensile strength, elongation and hardness values were related to the mean length of needle-like phase.     

Rare earth application for heat-resisting alloys

High-temperature oxidation resistance of Al2O3-and Cr2O3-forming heat-resisting alloys with rare earths(yttrium-implanted FeCrAl,-added FeCrAl,-added FeCrAlPt alloys,Y2O3-or CeO2-coated NiCrSi,yttrium-or lutetium-added NiCr and NiCrSi) was studied in oxygen at high temperatures,by mass gain measurements,mass change measurements,amount of spalled oxide,observation of surface appearance,X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe X-ray microanalysis(EPMA) and transmission electron microscopy(TEM).After oxidation at 1573 K for 18 ks in oxygen,oxide scale on FeCrAl alloy spalled from the entire surface,however,yttrium-implanted FeCrAl alloys showed good oxide adherence.After oxidation at 1473 K for 18 ks in oxygen,mass gain of FeCrAlY alloys decreased with increasing yttrium of up to 0.1 wt.% follwed by an increase with the yttrium content,and the mass gain of FeCrAl0.005Pt0.05Y alloy with appropriate additions of platinum and yttrium was lower than that of FeCrAl0.1Y alloy.Yttrium-added FeCrAl alloys showed good oxide adherence.TEM analysis revealed that the alumina/alloy interface of FeCrAl0.005Pt0.05Y alloy showed good coherency.The scale surface of FeCrAl alloy was rough,however,those of FeCrAlY and FeCrAlPtY alloys were smooth.Cyclic oxidation of NiCrSi,Y2O3-or CeO2-coated NiCrSi alloys was studied up to 10 cycles(1 cycle:300 s) at 1523 K in oxygen.Mass change of NiCrSi alloy increased up to 3 cycles and then decreased up to 10 cycles because of oxide spallation during cooling.On the other hand,mass change of Y2O3-or CeO2-coated NiCrSi alloy increased up to 10 cycles,and these alloys showed good oxide adherence.Granular Cr2O3 particles on Y2O3-coated NiCrSi alloy were in size smaller than these on CeO2-coated NiCrSi alloy.This result suggested that oxidation rate of Y2O3-coated NiCrSi alloy was lower than that of CeO2-coated NiCrSi alloy.After oxidation at 1473 and 1573 K for 18 ks in oxygen,mass gain of yttrium-or lutetium-added NiCr and NiCrSi alloys decreased.Oxide scales on NiCrS     

Solidification behavior, microstructure and tensile properties of ZK60-Er magnesium alloys

ZK60-Er (erbium) alloys were made by melting ZK60 and Mg-Er magnesium alloys (20 wt.% Er) in an electric resistance furnace. The contents of Er were 0, 0.5, 1, 2, 3 wt.%, respectively. The influence of Er on solidification behavior, microstructure, corrosion resistant and mechanical properties of ZK60 magnesium alloy was studied. The results showed that long rod-like γ phase (ErZn5) formed during solidification increased with increasing Er content in the range investigated, which resulted in the decrease of the amount of galvanic couplings between phase particles and alloy matrix and the marked improvement of corrosion resistant. It was also found that elongation of the alloys decreased with increasing Er content, but tensile strength of the alloys were improved by the addition of Er due to the strengthening effect of γ phases distributing along grain boundaries.     

Microstructure and mechanical properties of A356 alloy with yttrium addition processed by hot extrusion

The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that the addition of Y improves the microstructure of the as-cast alloy. The distribution of primary α-Al is uniform and orderly. The long needle-like eutectic Si phases and β-Fe phases turn to strips and short rods. When the content of Y increases to 0.2 wt%, the mean diameter of aAl(40.3 μm) and the aspect ratio of the eutectic Si phase(2.3) reach the minimum values, which are68.9% and 86.1% lower, respectively, than that of the alloy without Y addition. Under extrusion stress, the shape of the eutectic Si phase is changed from long rod-like to near grain-like after solution treatment.The size of the eutectic Si phase is significantly reduced. The needle-like β-Fe phases are squeezed and broken. The mechanical properties of the as-extruded alloy are significantly improved compared to the as-cast alloy. When the rare earth content is 0.2 wt%, the ultimate tensile strength, hardness and elongation of the alloy reach the maximum values, which are 328.2 MPa, 110.4 HV and 21.3%, respectively, and increase by 42.01%, 37.71% and 481.91%, respectively, in comparison to the as-cast alloy without Y addition.     

Influence of rare earth nanoparticles and inoculants on performance and microstructure of high chromium cast iron

The high chromium cast irons (HCCIs) with rare earth (RE) nanoparticles or inoculants were fabricated in the casting process. The phase compositions and microstructure were analyzed by X-ray diffraction (XRD) and optical microscopy (OM), respectively. The hardness and impact toughness were tested by Rockwel-hardmeter and impacting test enginery. And then, the morphology of fracture was researched by scanning electron microscopy (SEM). The results demonstrated that the phase compositions of HCCIs with addition of RE nanoparticles or inoculants which were M7C3 carbides + α-Fe did not change obviously. However, the prime M7C3 carbides morphology had great changes with the increase of RE nanoparticles, which changed from long lath to granular or island shape. When the content of RE nanoparticles was 0.4 wt.%, the microstructure of high chromium cast iron was refined greatly. The microstructure of carbides was coarser when the addition of RE nanoparticles was higher than 0.4 wt.%. The hardness and impact toughness of HCCIs were improved by addition of RE nanoparticles or inoculants. The impact toughness of HCCIs was increased 36.4% with RE nanoparticles of 0.4 wt.%, but the hardness changed slightly. In addition, the adding of RE nanoparticles or inoculants could reduce the degree of the brittle fracture. Fracture never seemed regular, instead, containing lots of laminates and dimples with the increase of the RE nanoparticles. The results also indicated that the optimal addition amount of the RE nanoparticles was 0.4%, under this composition, the microstructure and mechanical property achieved the best cooperation. In addition, through the study of erosion wear rate, when adding 0.4% RE nanoparticles into the HCCIs, the erosion wear rate got the minimum 0.32×10-3 g/mm2, which could increase 51.5% compared with that without any RE nanoparticles.     

Effect of combinative addition of mischmetal and titanium on the microstructure and mechanical properties of hypoeutectic Al-Si alloys used for brazing and/or welding consumables

Effects of mischmetal(RE) and/or Ti modifier on the microstructure including α-Al dendrites, eutectic Si phases and other secondary phases of Al-Si brazing and/or welding alloys were investigated by differential scanning calorimetry(DSC), optical microscopy(OM), scanning electron microscopy(SEM). The DSC results showed that an addition of RE decreased the eutectic temperature and caused supercooling, promoting the nucleation of eutectic Si crystals. In addition, the maximum temperature of the first endothermic peak varied with the different RE contents, which had a good correlation with the microstructural modification of the eutectic Si phase. The α-Al dendrites were well refined by increasing the cooling rate or adding 0.08 wt.% of Ti. When 0.05 wt.% RE was added to the Al-5Si-0.08 Ti alloy, the morphology of eutectic Si phase was transformed from coarse platelet to fine fibers and the mechanical properties of the resulting welding rod were well improved. Whereas, when excess RE was added, a large number of β-Fe phases appeared and the aspect ratios of β-Fe phases increased. The morphologies and chemical components of two kinds of RE-containing intermetallic compounds(IMCs) were also discussed.     

Effect of neodymium,gadolinium addition on microstructure and mechanical properties of AZ80 magnesium alloy

The microstructure and mechanical properties of AZ80 magnesium alloys with varying Nd, Gd contents were investigated. The results revealed that the as-cast microstructure of AZ80 alloy was composed of α-Mg matrix and divorced eutectic β-Mg_(17)Al_(12) phases. The fraction of Mg_(17)Al_(12) phase was reduced when 0.6 wt.% Nd was added, and new rod-shaped Al_(11)Nd_3 phase and small block-shaped Al-Nd-Mn phase appeared. With Gd addition, the Gd elements mixed with Nd to form rare earth phases. New block-shaped Al_2Gd and Al_2Nd phases which were collectively called Al_2RE phases were observed in the microstructure with more than 0.6 wt.% Gd addition. Moreover, the addition of Gd could promote the precipitation of block-shaped Al_2RE phase, and inhibit the original rod-shaped Al_(11)Nd_3 phase. The AZ80-0.6Nd-0.6Gd alloy exhibited the optimal mechanical properties among all the experimental alloys, in which the tensile strength, yield strength and elongation were 215, 145 MPa and 8.33%, respectively.     

Microstructures and Mechanical Properties of Al89Gd7Ni3Fe Alloy Extruded from Its Amorphous Powders

The microstructures and mechanical properties of Als9 GdTNi3Fe alloy extruded from its amorphous powder were investigated at different temperatures. Devitrification process of amorphous phase was also analyzed. As a result, the microstructure of the extruded alloy consists of fee α-Al, binary intermetallic Al3Gd and ternary intermetallic r l phase. The grain size of α-Al is fine. The intermetallic Al3Gd exists as equiaxed particle and τ1 phase appears rod like.     

Effect of ball milling on hydrogen storage of Mg3La alloy

Hydrogen storage and microstructure of ball milled Mg3La alloy were investigated by X-ray diffraction and pressure-composition-isotherm measurement. The ball milled Mg3La alloy could absorb hydrogen up to 4wt.% at 300 ℃ for the first time, along with a decomposing course. Following tests showed that the average reversible hydrogen storage capacity was 2.7wt.%. The enthalpy and entropy of dehydrogenation reaction of the decomposed ball milled Mg3La and hydrogen were calculated. XRD patterns indicated the existence of MgH2 and LaH3 in the decomposed hydride and the formation of Mg when hydrogen was desorbed. After the first hydrogenation, all the latter hydrogenation/dehydrogenation reactions could be taken place between Mg and MgH2. The ball milled Mg3La alloy exhibited better hydriding kinetics than that of the as-cast Mg3La alloy at room temperature. The kinetic curve could be well fitted by Avrami-Erofeev equation.     

A comparison between DCCAE and conventional extrusion of Mg-9.5Li-3Al-1.6Y alloy

Double change channel angular extrusion(DCCAE) was performed in dual-phase Mg-9.5Li-3Al-1.6Y(wt.%) alloy to develop fine-grained microstructures. The microstructure evolution during DCCAE and conventional extrusion(CE) was investigated. The microstructure of the extruded dual-phase Mg-Li alloy consisted of recrystallized β-Li grains, banded α-Mg phases, and Al_2Y phases distributed in β-Li phases and phase-interface uniformly. Compared with CE, the specimens after DCCAE had smaller β-Li grain size(3–5 μm by the DCCAE and 6–10 μm by the CE) and the α-Mg phases were refined during the DCCAE. The distribution of the Al2 Y phases was improved a lot by DCCAE. Furthermore, the specimens after DCCAE had better tensile strength than conventional extrusion ones.     

Study on microstructure and mechanical properties of as-cast Mg-Sn-Nd alloys

Microstructure, tensile properties and compressive creep behaviors of Mg-(1.65-11.52) wt.% Sn-2 wt.% Nd alloys were studied in this paper. The microstructure of the as-cast Mg-Sn-Nd alloys consisted of dendritic α-Mg, Mg2Sn and Mg-Sn-Nd ternary phase containing rare earth element. The highest ultimate tensile strength of 140 MPa and percentage elongation after fracture of 9.7%, were achieved with a composition of Mg-8.23 wt.% Sn-2 wt.% Nd. The compressive creep resistance of Mg-8.23 wt.%Sn-2 wt.% Nd alloy w...     

Preparation and characterization of Mg-6Li and Mg-6Li-1Y alloys

Mg-6Li and Mg-6Li-1Y (wt.%) alloys were prepared using permanent model casting method, and microstructure and mechanical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM), energy dis-persive spectrometry (EDS), transmission electron microscopy (TEM), etc. The results showed that α-Mg and ?-Li phases existed in both al-loys, and there was also Y-enriched phase in Mg-6Li-1Y alloy. The composition of Y-enriched phase was near to the ma...     

强磁场对铁基合金相变温度和显微组织的影响

The effect of a high magnetic field up to 30 T on phase transformation temperature and microstructure of Fe-based alloys has been reviewed. A high magnetic field accelerates ferrite transformation, changes the morphology of the transformed microstructures and increases the As and A1 temperature. In a magnetic field of 30 T, the A1 temperature increases by about 37.1℃ for Fe-0.8C, the A3 temperature for pure Fe increases by about 33.1 ℃. The measured transformation temperature data are not consistent with calculation results using Weiss molecular field theory. Ferrite grains are elongated and aligned along the direction of magnetic field in Fe-0.4C and Fe-0.6C alloys by ferrite transformation, but elongated and aligned structure was not found in pure Fe, Fe-0.05C alloy and Fe-1.5Mn0.11C-0.1V alloy.