Microstructure and Mechanical Properties of TiAl-based Alloy

Two phases gamma titanium aluminide alloy,Ti-46.5Al-2.5V-1Cr.was investigated to characterizemicrostructures and to define the microstructure/mechanical property relationship.Many kinds ofmicrostructure of gamma and α_2 phases were obtained by heat treatments in the α+γ,α_2+γ and αfields.The effects of microstructure on tensile properties,fracture toughness and J-R resistancecurve at room temperature,were systematically studied.The experimental results showed that themicrostructure had a strong effect on mechanical properties,The duplex microstructure produced byheat treatment at 1250℃×4 h with controlled cooling resulted in the highest ductility of 4.8% tensileelongation,low fracture toughness and crack growth resistance.The fully lamellar microstructureproduced by heat treatment in the α field having large grain sizes resulted in the highest fracturetoughness but the lowest ductility.     

Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

1. IntroductionAluminum alloy for aircraft industry is requiredto maintain microstructure stabilityt strength andtoughness at temperatures ranging from 100 to 200'Cor even higher. Some rapidly solidified powder metallurgy (RS/PM) experimental alloys, such as ALFe-VSi alloyt have good mechanical properties up to 300'C.But the alloys produced by rapid solidiflcation processing tend to be relatively more costly and moredifficult to prepare than wrought materials fabricatedfrom ingots[1]. Acc…     

Effect of Si,Mn and Al on the Microstructure and Mechanical Properties of ADI Weld Metal

The effects of Si,Mn and Al on the microstructure and mechanical properties of ADl weld have been studied.The microstructure of ADl weld metal mainly consists of bainitic ferrite and retained austenite.Mechanical properties of Adl weld increase with increasing Si content,but an excess of Si(3.79%) results in decreasing the austemperability owing to decreasing the carbon content of the matrix austenite.Mn increases the retained austenite volume fractio,but the ductility and impact toughness of weld obviously decrease with increasing Mn content because of increased amount of martenite and twin martenite.In the range of 0.13%-0.64%Al ,increasing Al content favours improving the mechanical properties of ADl weld.Therefore,it is very important to select suitable Si,Mn and Al contents to improve mechanical properties of ADl weld .     

Effect of Nb on the Microstructure and Mechanical Properties of Cast NiAl-Cr（Mo） Eutectic Alloy

The microstructure and mechanical behaviors of NiAl-28Cr-5Mo-1Nb eutectic alloy were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and compression tests, respectively. The alloy is mainly composed of three phases, which are the gray lamellar Cr（Mo） plate, black NiAI matrix and semicontinuously distributed Cr2Nb-type Laves phase. Through Nb addition, NiAl-Cr（Mo）/Nb alloy exhibits a reasonable balance of high temperature strength and room temperature compression ductility and its mechanical behaviors are superior to the NiAl-28Cr-6Mo eutectic alloy at all temperature. The elevated temperature compression deformation behavior of NiAl-Cr（Mo）/Nb alloy can be properly described by power-law equation.the National High Technology Committee of China （No. 863-715-005-0030） for financial supports.     

Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics

Densified Yb-, Y-, Dy-, Sin- and Nd-α-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations （Yb3＋, y3＋ and Dy3＋） are fully composed of α-Sialon, while in the larger cations （Sm3＋ and Nd3＋） doped ceramics also exist a few intergranular phase Mt （Re2Si3-xAlxO3＋xN4-x） in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa·m^1/2.     

Mechanical Properties and Microstructure of Diamond–SiC Nanocomposites

A bulk composite material close in hardness to diamond was fabricated from nanocrystalline diamond and SiC. The mechanical properties and microstructure of the composite were studied. Young's modulus of the composite is found to be notably lower than the one following from the additivity rule, which is attributable to the influence of structural defects present in the interfacial zone between SiC and diamond. SiC consists of nanometer-scale grains near the interface and submicron grains in the pores.     

Microstructure and Mechanical Properties of Overcast 6101–6101 Wrought Al Alloy Joint by Squeeze Casting

The wrought Al alloy–wrought Al alloy overcast joint was fabricated by casting liquid 6101 Al alloy onto6101 Al extrusion bars and solidifying under applied pressure.The joint interfacial microstructure was investigated;the effect of applied pressure on the microstructure and mechanical properties was evaluated.The mechanism of joint formation and mechanical behaviors of both squeeze cast 6101 and 6101–6101 overcast joint material were analyzed.The results show that with the application of pressure during solidification process,wrought Al alloy 6101 could be cast directly into shape successfully.Excellent metallurgical bonding was then formed in the overcast joint by electro-plating 6101 solid insert with a layer of zinc coating,and a transition zone formed in the joint region.During the tensile test,the fracture occurs in the 6101 solid insert part with the ultimate tensile strength(UTS)of 200 MPa,indicating that the strength of the overcast joint is higher than 200 MPa,and the tensile strength of overcast joint material is independent on the magnitude of applied pressure.For Al–Al overcast joint material,if a clean and high strength joint is formed,the UTS and yield strength(YS)are determined by the material with the lower value,while for EL,the value is determined by the length proportion and the stress–strain behavior of both components.     

Microstructure and Mechanical Properties of Two-phaseTiAl Alloys in Lamellar Form

In two-phase TiAl alloys, the lamellar structures are of special interest and importance since they are so common and persistent. not only under as-cast conditions but also after thermal treatment. However. the lamellar structures are still poor in ductility,although they are beneficial for toughness and high temperature strength. This article will review the recent progress made in understanding the basic mechanical properties of the γ and α2 phases which comprise the two-phase alloys in Iamellar form, and discuss how an improved balance of strength and ductillty in the lamellar form may be achieved     

Effect of Different Aging Processes on the Microstructure and Mechanical Properties of a Novel Al–Cu–Li Alloy

The effects of different aging processes on the microstructure and mechanical properties of a novel Al–Cu–Li alloy have been investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the tensile properties of a novel Al–Cu–Li alloy are sensitive to aging processes, which correspond to different microstructures. σ(Al_5Cu_6Mg_2) and T_1(Al_2CuLi) phases are the major precipitates for the alloy in T6 aging condition(165 ℃/60 h). After duplex aging condition(150 ℃/24 h + 180 ℃/12 h), σ, θ'(Al_2Cu) and T_1 phases are detected. Only the T_1 phases can be found in the T8 state alloy(6% pre-strain+135 ℃/60 h). The failure modes of alloy in T6 and duplex aging conditions are dimple-intergranular fracture, while typical quasi-cleavage fracture in T8 condition.     

Hot Extrusion Effect on the Microstructure and Mechanical Properties of a Mg–Y–Nd–Zr Alloy

Strength of Materials - Mg–Zn–Y–Nd alloy was prepared by casting and hot extrusion. The microstructure and mechanical properties of OM, SEM, XRD, TEM, and tensile tests were...     

Effect of Melt Processing Programme on Microstructure and Properties of YBCO Thick Films

The screen printing technique was used in the fabrication of YBa₂Cu₃O_7−σ (YBCO) superconducting thick films on yttria stabilised zirconia (YSZ) substrates. Different slow cooling rates were used in the preparation of YBCO thick films after fast cooling from the melt processing temperature. The effects of the melt processing programme on texturing, microstructure and superconducting properties of the melt processed YBCO films were studied. Slow cooling rates between 1005 and 990 °C were effective in increasing the interaction of viscous molten with reduced film/substrate, and hence a relatively large grain size has been obtained. Moreover, different c-axis texturing ratios and grain morphologies were observed.     

Effect of Milling Time on the Microstructure and Tensile Properties of Ultrafine Grained Ni–SiC Composites at Room Temperature

Bulk metallic nickel–silicon carbide nano-particle(Ni–Si CNP) composites, with milling time ranged from8 to 48 h, were prepared in a planetary ball mill and sintered using a spark plasma sintering(SPS)furnace. The microstructure of the Ni–Si CNP composites was characterized by transmission electron microscopy(TEM) and their mechanical properties were investigated by tensile measurements. The TEM results showed well-dispersed Si CNP particles, either within the matrix, between twins or along grain boundaries(GB), as well as the presence of stacking faults and twin structures, characteristics of materials with low stacking fault energy. Dislocation lines were also observed to interact with the Si CNP which were plastically nondeformable. A synergistic relationship existed between Hall–Petch strengthening and dispersion strengthening mechanisms, which was shown to greatly influence the mechanical properties of the Ni–Si CNP composites. Both the maximum yield and tensile strengths were found in the Ni–Si CNP composite with a milling time of 48 h, whereas the increased rate of strengths drastically decreased in material milled above 8 h due to the significant Si CNP agglomeration. The ball milling process resulted in the formation of nano-scale, ultra-fine grained(UFG) Ni–Si CNP composites when the milling time was extended for longer periods, greatly strengthening these materials. The sharp decrease in elongation percentages, however, should be comprehensively considered before irreversible inelastic deformation.     

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina-fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600℃. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500℃ for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2 ,the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate (Al2O3-TiO2:Al2TiO5 ). The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.     

Microstructure and Mechanical Properties of ZrO_2-Ni Functionally Gradient Material

The fabrication. microstructure and mechanical properties of ZrO2-Ni functionally gradient materials (FGM ) have been studied. FGM as well as non-FG M of ZrO2-Ni system was developed by powder metallurgical process. X-ray diffractometer (XRD ). electron probe microanalyzer (EPMA), scanning electron microscope (SEM ) and optical microscope were employed to investigate the crystalline phases. chemical composition and microstructure Experimental results demonstrate that the composition and microstructure of ZrO2-Ni FGM have the expected gradient distribution. There are no distinct interfaces in the FGM due to the gradient change of components. that is, the constituents are continuous in microstructure everywhere. Moreover, Vickers hardness and flexural strength were measured for the common composites as a function of composition. It is made clear that the mechanical properties of the FGM vary corresponding to the constitutional changes as well     

Microstructure and Mechanical Properties of TiB-Containing Al–Zn Binary Alloys

The microstructure and mechanical properties of newly developed Al–35Zn cast alloys with Ti B re?ner addition were evaluated by X-ray diffractometry, optical microscopy, and scanning electron microscopy coupled with energy dispersive spectrometry. The microstructure of these alloys featured α-Al dendrites surrounded by Al–Zn(α + η) eutectic structures. After the addition of Ti B re?ner, the alloy grain sizes decreased, and its morphology abruptly changed from dendritic to equiaxed grains. Such an improved microstructure of the modi?ed alloys was accompanied by a signi?cant increase in the tensile strength and elongation percentage compared to those of the Al–Zn or Zn–Al-based alloys. The results showed that with the increase of Ti B content up to 0.05%, the morphology of α-Al dendrites and α + ηphases changed from coarse dendrite and lamellar structures into independent and ?ne ones. Based on these results, the effect of Ti B re?ner addition on the microstructure and mechanical properties of the Al–35Zn binary alloys was investigated.     

Effect of Cold Plasma Treatment on the Mechanical Properties of RTM Composites

Cold plasma technology was used to treat the surface of carbon fibers braided by PET in this paper and SEM was used to analyze the fracture microstructure of composite interlaminar shear stress (ILSS). The result shows that the surface polarity of carbon fibers was modified by cold plasma treatment, which increases the impregnation of PET braided carbon fibers during the process of resin flowing, improves the interfacial properties of RTM composites, and therefore enhances the mechanical properties of the KTM composites.     

Microstructure and Mechanical Properties of Al-4.9Ni-4.9Ti Alloy Prepared by Mechanical Alloying

Mechanically alloyed Al-4.9Ni-4.9Ti powders were prepared by milling mixed aluminium, titanium and nickel powders, and then consolidated by hot hydrostatic extrusion. The microstructures of milled powders and extruded bars were characterized by X-ray diffraction and transmission eIectron microscopy observation. The results show that mechanical alloying and consolidating processes have great effects on the microstructures and mechanical properties of extruded materials. Polycrystalline materials having an ultrafine grain size may be prepared by mechanical alloying. The strength and thermal stability are improved with the increasing of processing time of mechanical alloying, since grain size decreases and volume fraction of dispersoids increases as milling time increased     

Microstructure and Mechanical Properties of Dy-α-sialon/Nano-size SiC Composites

The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature