Consolidation and Compression Property of Nanocrystalline NiAl Synthesized by Mechanical Alloying

The mixture of pure nickel and aluminum powders in the composition of Ni50AI50 was subjected to high energy ball milling. The high energy ball milling to 30 h resulted in the formation of a nanocrystalline NiAl with a grain size of about 10 nm. The as-milled NiAl powder was hot-pressed and the compact with a density of 90% was obtained. It was showed that heating to900℃ and holding for more than 2 h failed to induce the coarsening of the fine nanocrystalin the material, the tendency of grain growth was weak. Compression testing showed that thecompression ductility at room temperature reached about 7%. The ductility increased with theexperimental temperature while the strength decreased drastically at elevated temperature.     

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     

Microstructural Evolution during Mechanical Milling of Rapidly Solidified Al–14Ni–14Mm1 Alloy Powders

Microstructural evolution in gas-atomized Al–14 wt%Ni–14wt% Mm alloy powders was studied during mechanical milling. It was noted that the as-solidified particle size of 200 m increases up to 72 h of milling and, subsequently, there was continuous refinement to 20 m on milling to 200 h. Two microstructurally different zones—Zone A, which is featureless, and Zone B, which has the structure of the as-solidified powder—were noted. The thickness of the Zone A increased with increasing milling time at the expense of Zone B. Zone A was found to be much harder than Zone B and, consequently, crack formation, eventually leading to microstructural refinement, was observed to start in the relatively weaker Zone B.     

Improving Densification and Mechanical Properties of FeAl/TiC Composites by Addition of Ni

FeAl/TiC composites were fabricated by pressing blended elemental powders,The effects of Ni-doping on the densification and mechanical properties of the compostes were studied.Results show that density of the composites decreases with the content of TiC increasing ,and the addition of Ni significantly improves the densification process by enhancing mass transfer in the bonding phase,The mechanical properties of the composites are closely related with their porostiy ,Besides increasin the density of the comosites,the addition of Ni improves the mechanical properties by other three effects:solution-strengthening the bonding phase,strengthening the FeAl-TiC interface and increasing ductile fracture in FeAl phase.     

Measurements of Microstructural, Mechanical, Electrical, and Thermal Properties of an Al–Ni Alloy

The Al–7.5 wt% Ni alloy was directionally solidified upwards with different temperature gradients, $G$ ( $0.86\,\text{ K}~{\cdot }~ \text{ mm}^{-1}$ to $4.24\,\text{ K}~{\cdot }~\text{ mm}^{-1})$ at a constant growth rate, $V$ ( $8.34\,\upmu \text{ m}~{\cdot }~\text{ s}^{-1})$ . The dependence of dendritic microstructures such as the primary dendrite arm spacing ( $\lambda _{1}$ ), the secondary dendrite arm spacing ( $\lambda _{2}$ ), the dendrite tip radius ( $R$ ), and the mushy zone depth ( $d$ ) on the temperature gradient were analyzed. The dendritic microstructures in this study were also compared with current theoretical models, and similar previous experimental results. Measurements of the microhardness (HV) and electrical resistivity ( $\rho $ ) of the directionally solidified samples were carried out. Variations of the electrical resistivity ( $\rho $ ) with temperature ( $T$ ) were also measured by using a standard dc four-point probe technique. And also, the dependence of the microhardness and electrical resistivity on the temperature gradient was analyzed. According to these results, it has been found that the values of HV and $\rho $ increase with increasing values of $G$ . But, the values of HV and $\rho $ decrease with increasing values of dendritic microstructures ( $\lambda _{1}, \lambda _{2}, R,$ and $d$ ). It has been also found that, on increasing the values of temperature, the values of $\rho $ increase. The enthalpy of fusion ( $\Delta {H}$ ) for the Al–7.5 wt%Ni alloy was determined by a differential scanning calorimeter from a heating trace during the transformation from solid to liquid.     

Insights into Phase Evolution and Mechanical Behavior of the Eutectoid Ti–6.4(wt%)Ni Alloy Modified with Fe and Cr

Titanium alloys gain increasing importance in industry due to the expansion of advanced manufacturing technologies such as additive manufacturing. Conventional titanium alloys processed by such technologies suffer from formation of large primary grains and anisotropy of mechanical properties. Therefore, novel alloys are required. Herein, the effect of ternary alloying elements Fe and Cr on the Ti–6.4(wt%)Ni eutectoid system is investigated. Both elements act as eutectoid formers. Fe and Cr show sluggish transformation behavior, whereas Ni is an active eutectoid-forming element. Thereby, sluggish refers to slow and active to fast transformation kinetics. The focus of this work is on the combined addition of such elements studied under different heat-treatment conditions. It is shown in the results that largely varying microstructures can be generated resulting in hardness values ranging from 239 to 556 HV_0.1. Moreover, the formation of a substructure within the α phase of direct aged alloys is observed. The formation mechanism of this substructure is investigated in detail. The mechanical properties are discussed based on the microstructural characteristics. The presence of intermetallic Ti₂Ni phase increases the Young's modulus, whereas the presence of ω phase results in embrittlement. The results shed light upon the complex phase formation and decomposition behavior of titanium alloys based on Ti–6.4Ni.     

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.     

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.     

Formation of Omega-like Nanocrystalline in the Melt-Spun Nd_(85)Al_(15) Alloy by Phase Transformation

Microstructure and subsequent phase transformations on heating of the melt-spun Nd85Al15 alloy have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The melt-spun Nd85Al15 alloy shows two-stage transformation processes as follows: amorphous+72 nm supersaturated bcc-Nd(AI) solid solution-7 nm omega-like phase-AlNd3+hexagonal Nd. The activation energies for the first and second transformation were found to be 100 kJ/mol and 188 kJ/mol, respectively. The formation mechanism of nanoscale omega-like phase is discussed.     

Surface Characterization of Ni_(64)P_(20)Fe_(16)Amorphous Alloy by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy

The nature of the native oxides formed on thesurface layer of amorphous alloy Ni_(64)P_(20)Fe_(16)hasbeen studied by X-ray photoelectron spectroscopy(XPS)and Auger electron spectroscopy(AES)withdepth profiling by ion bombardment.There aregreat distinctions in compositions and chemicalstates between the surface layer and the bulk.Themain constituents Ni,P and Fe are lower in the sur-face layer,and they are mostly in oxidized states,whereas C,O and N are enriched in the surface lay-er.The thickness of surface oxide layer isapproximately 20 nm,this layer was assumed to beof great significance to various properties of amor-phous alloy Ni_(64)P_(20)Fe_(16),expecially to the chemicaland catalytic properties.Experiments proved thattransitional element Fe cannot improve oxidationresistance of the amorphous Ni-P system.     

Hydrogen Permeation and Diffusion in Amorphous Alloy Ni_(68)Cr7_Si_8B_(14)Fe_3 at Elevated Temperature

The behaviour of hydrogen permeation and diffusion in amorphous alloy Ni68Cr7Si8B14Fe3 hasbeen investigated by an ultrahigh vacuum gas permeation technique. A comparison experimentwas carried out between the as-quenched and annealed States (400℃/2h) of the amorphousalloy. The results show that, for both states of the amorphous alloy in the temperature rangeof 200～350℃, the diffusivity and permeability of hydrogen are in agreement with Arrheniusrelationship, there does not exist H-trapping effect, and the activation energies of diffusion andpermeation almost keep the same.     

Effect of Trace Elements P and Si(Mn) on Hydrogen Embrittlement of JBK-75 Alloy

High purity hot hydrogn charging at high temperature was used to investigate the hydrogen embrittlement (HE) of JBK-75 alloys with different contents of P and Si(Mn). The results indicated that by lowering P content, the size and distribution γ' precipitate became more homogeneous and the precipitation of stable phase η was retarded, thus the hydrogen resistant properties of the alloy wes obviously improved; however, when Si(Mn) content was lowered together with P, though the size and density of γ' were also homogeneous and no η phase was observed, formation of some micro twin around grain boundaries was found to be detrimental to the hydrogen performance of the alloy. and hydrogen induced loss of area reduction was very high. Therefore, to improve the hydrogen resistant properties of the alloy, P content should be lowered while certain amount of Si(Mn) should be kept     

Microstructure and Mechanical Properties of C/(ZrB2–SiC) Composites Produced from Ceramic Ribbons

Inorganic Materials - We have studied the morphology, texture, and bending strength of Cf/(ZrB2–SiC) continuous carbon fiber-reinforced ceramic composite materials prepared by a new method...     

Formation and Properties of Nanocrystalline (Fe_(0.99)Mo_(0.01))_(78)Si_9B_(13) Alloy

Polycrystalline Fe-Mo-Si-B alloys with grains sized from 15 to 200 nm were prepared by means ofthe crystallization method. A critical phenomenon was observed in the variations of microhardnessand electrical resistivity with respect to the annealing temperature. The critical temperature is 893 Kwhich corresponds to the average grain size of 45 nm.     

Microstructure and Mechanical Properties of 06Cr13Ni4Mo Steel Treated by Quenching–Tempering–Partitioning Process

A heat treatment process,quenching-tempering-partitioning(Q-T-P),has been applied to a low carbon martensitic stainless steel 06Cr13Ni4 Mo.By using this process,ultrafine reversed austenite can be obtained at room temperature.The microstructures of the reversed austenite and the martensite matrix were characterized by transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS)in detail.The results show that the ultrafine reversed austenite is enriched in Ni resulting in the austenite stability at room temperature.Two new types of nano-scale carbide precipitates are found in the martensite matrix.Detailed analysis suggests that the two nano-scale precipitates can be identified asω phase and λ phase carbides,respectively.The orientation relationship between the ω phase and matrix is[011]α//[2110]ω and(211)α//(0110)ω,while that between the λ phase precipitate and matrix is[011]α//[0001]λ and(200)α//(1210)λ.For the present steel,the ultrafine reversed austenite and carbide precipitates obtained by Q-T-P treatment provide a good combination of high strength and toughness.     

Corrosion Behaviour of Ni–Co Alloy Coatings at Kish Island (Marine) Atmosphere

In this study, the corrosion behaviour of Ni-Co alloys with low Co content, electroplated on steel substrate in sulphate bath, was investigated. The morphology of coatings was studied by optical and SEM microscopy. The corrosion products were analyzed using EDX. The results showed that Ni–1%Co coatings had a better corrosion resistance 0·30, 0·92 and 3·75 mpy for atmospheric, salt spray and polarization tests, respectively. These are 0·41, 1·20 and 5·40 mpy for pure nickel coatings that indicate the least corrosion resistance. Surface analysis revealed the presence of oxides, sulphides and chlorides in corrosion products.