Kinds Of Alloys Research Articles

Influence of chemical composition on martensitic transformation of MnNiIn shape memory alloys

The most extensively studied Heusler alloys are those based on the Ni–Mn–Ga system. However, to overcome the high cost of Gallium and the generally low martensitic transformation temperature, the search for Ga-free alloys has been recently attempted, particularly, by introducing In, Sn or Sb. In this work, two shape memory alloys, Mn50Ni50−xInx (x = 7.5 and 10), were obtained by rapid solidification. We outline their structural and thermal behaviour. The structural austenite–martensite transformation was checked by calorimetry. The transformation temperatures decrease as In content increases. The same pattern is reflected in entropy and enthalpy changes linked to transformation. The control of the valence electron by atom (e/a) determines the transformation temperatures range in this kind of alloys, and it is possible to develop alloys that can be candidates in applications such as sensors and actuators. In addition, X-ray diffraction was performed to verify the crystalline structure at room temperature.

Differential Scanning Calorimetry Studies on Ni-Ni<sub>3</sub>B Alloys

Solidification behaviors of hypoeutectic Ni-3.3wt% B and hypereutectic Ni-4.5wt% B alloys were investigated by using differential scanning calorimetry (DSC) technology. Experimental results showed that the solidification behaviors are similar for the two kinds of alloys with small sizes, i.e. three transformed peaks (corresponding to L→α-Ni, L→Ni-Ni23B6and Ni23B6→Ni+Ni3B, respectively) appear in the cooling curves, and three phases (primary phase α-Ni, rod eutectic and dot precipitates) appear in the microstructures, which are different from that of the alloys with large sizes. It can be attributed to the fact that the nucleation of α-Ni and Ni23B6phases are easier than that of Ni3B phase for small samples of hypoeutectic and hypereutectic Ni-Ni3B alloys.

Preparation and Magnetic Properties of Nanocrystal Bulk SmCo<sub>7</sub> Magnets

Two kinds of 2:17R Sm-Co alloys, Sm2(Fe,Cu,Zr,Co)17 and pure binary Sm2Co17 were prepared, and the amorphous powder was prepared by high-energy ball milling Sm-Co alloys. The bulk nanocrystalline SmCo7 was prepared by hot-pressing the amorphous powder, and the magnetic properties and phase composition were studied. Initial Sm2(Fe,Cu,Zr,Co)17 showed a large value of coercivity while the pure Sm2Co17 almost showed no coercivity. However, after ball milling the grain size of alloys decreased dramatically until completely amorphous. Two kinds of alloys showed the different phase composition and magnetic properties after hot-pressing. It was found that the pure Sm2Co17 bulk magnet showed a high coercivity Hc and had the 1:7H phase. On the other hand, the Sm2(Fe,Cu,Zr,Co)17 showed high saturation magnetization Ms and very low Hc since the Fe-Co and Sm2Co3 phase were precipitated from the alloy.

Effect of Li atom infiltration by the way of electro-osmosis on electrochemical properties of amorphous Mg65Ni27La8 alloy used as negative electrode materials for the nickel–metal hydride secondary batteries

The Mg65Ni27La8 alloy is synthesized by arc melting and subsequent melt-spinning technique, then Li atoms are infiltrated into this alloy material by the way of electroosmosis. The structure of the above two kinds of alloys is characterized by X-ray diffraction and scanning electron microscopy. Furthermore, electrochemical properties of two alloy electrodes are investigated systematically. Electrochemical studies indicate that negative electrode prepared by the Mg65Ni27La8-Li alloy possesses the best discharge capacity (693.8mAh/g) and cycling stability (83.2% after 30cycles) at a current density of 30mA/g, which is higher than that of Mg65Ni27La8 alloy electrode. Compared with the Mg65Ni27La8-Li alloy, the Mg65Ni27La8 alloy shows better discharge capacity of 571.9mAh/g and lower cycling stability (70.2% after 30cycles), which explains the structure evolution of amorphous ribbon that is responsible for the decay of discharge capacity. In addition, we also study the electrochemical reaction kinetics of Mg65Ni27La8-Li alloy electrodes.

INFLUENCE OF Pt ON THE CREEP RUPTURE PROPERTIES OF Ni-BASED SINGLE CRYSTAL SUPERALLOY

The Ni- based single crystal superalloys are considered to be the major materials for advanced areo- engine blades. In order to improve the high temperature properties of Ni- based single crystal superalloys,many refractory elements are introduced into this kind of alloys. Recently Pt has been suggested to be the alloying elements of advanced Ni-based single crystal superalloys. However, there are no researches for the effects of Pt on creep rupture properties of advanced single crystal superalloys. In this work, the influence of Pt element on the creep rupture properties of a Re-containing single crystal superalloy was investigated. The high-temperature creep rupture properties of the Pt-containing Ni-based single crystal superalloy at 1100 ℃, 180 MPa and 1000 ℃, 310 MPa were investigated. The deformation microstructure and the morphology of dislocations were studied by SEM and TEM.The results show that the creep rupture life of Pt-containing superalloy decrease slightly at 1100 ℃, 180 MPa and decreased obviously at 1000 ℃, 310 MPa. The fracture models of different alloys are all ductile fracture, and many irregular microviods and microcracks can be observed in the fracture surfaces. After high temperature creep deformation, regular dislocation networks formed at the g/g' interfaces. The differences of creep rupture properties among those alloys are that Pt element may promote the formation of TCP phase, and the interface between the TCP phase and g matrix may be favorite sites of the initiation of microvoids and microcracks.

LASER INDUCED - BREAKDOWN SPECTROSCOPY FOR QUANTITATIVE Sn ANALYSIS IN Zr BASED ALLOYS

Abstract Laser induced breakdown spectroscopy (LIBS) calibration curves for ZrSn alloys were obtained. Relationships between the atomic emission lines present in the spectra and the Sn concentration of the samples showed a linear behavior. Also Zy-2 standards were measured to contrast the behavior of the technique in different kind of alloys. The choice of proper Sn and Zr lines and the equipment's parameters, such as “integration start delay” and the spectrometer height, were fundamental to enhance the measurements. All samples were analyzed with X-ray fluorescence for a precise determination of their Sn concentration.

Study on surface relief related to reverse martensitic transformation in Mn-based high-temperature antiferromagnetic shape memory alloy

Evolution of surface relief and its intrinsic mechanism associated with martensitic transformation (MT) during heating and cooling in Mn79.5Fe15.6Cu4.9 high-temperature antiferromagnetic shape memory alloy (SMA) have been investigated in nano-scale by means of in-situ atomic force microscopy (AFM), X-ray diffraction (XRD), and dynamic mechanical analyzer (DMA). Experimental results show that the N-type surface relief originates from the reverse MT and is completely made of matrix which is different from the conventional ones. The reverse MT exhibits untwinning shear and the reverse shearing of twinned martensites mainly contribute to the surface relief. The measured surface relief angles are less than 1°, which are determined by the small difference of lattice constants between fcc and fct structures. Surface relief has a good recovery property because of the crystallographic reversibility rule in SMAs, implying that this kind of alloy has a good surface morphology memory effect.

Effect of metal primers and tarnish treatment on bonding between dental alloys and veneer resin.

PURPOSEThe aim of this study was to evaluate the effect of metal primers on the bonding of dental alloys and veneer resin. Polyvinylpyrrolidone solution's tarnish effect on bonding strength was also investigated.MATERIALS AND METHODSDisk-shape metal specimens (diameter 8 mm, thickness 1.5 mm) were made from 3 kinds of alloy (Co-Cr, Ti and Au-Ag-Pd alloy) and divided into 4 groups per each alloy. Half specimens (n=12 per group) in tarnished group were immersed into polyvinylpyrrolidone solution for 24 hours. In Co-Cr and Ti-alloy, Alloy Primer (MDP + VBATDT) and MAC-Bond II (MAC-10) were applied, while Alloy Primer and V-Primer (VBATDT) were applied to Au-Ag-Pd alloys. After surface treatment, veneering composite resin were applied and shear bond strength test were conducted.RESULTSAlloy Primer showed higher shear bond strength than MAC-Bond II in Co-Cr alloys and Au-Ag-Pd alloy (P<.05). However, in Ti alloy, there was no significant difference between Alloy Primer and MAC-Bond II. Tarnished Co-Cr and Au-Ag-Pd alloy surfaces presented significantly decreased shear bond strength.CONCLUSIONCombined use of MDP and VBATDT were effective in bonding of the resin to Co-Cr and Au-Ag-Pd alloy. Tarnish using polyvinylpyrrolidone solution negatively affected on the bonding of veneer resin to Co-Cr and Au-Ag-Pd alloys.

Laser Induced – Breakdown Spectroscopy for Quantitative Sn Analysis in Zr Based Alloys

Laser induced breakdown spectroscopy (LIBS) calibration curves for ZrSn alloys were obtained. Relationships between the atomic emission lines present in the spectra and the Sn concentration of the samples showed a linear behavior. Also Zy-2 standards were measured to contrast the behavior of the technique in different kind of alloys. The choice of proper Sn and Zr lines and the equipment's parameters, such as “integration start delay” and the spectrometer height, were fundamental to enhance the measurements. All samples were analyzed with X-ray fluorescence for a precise determination of their Sn concentration.

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Abstract Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

Elevated-temperature mechanical properties and thermal stability of Al-Cu-Mg-Ag heat-resistant alloy

The elevated-temperature mechanical properties and thermal stability of Al-Cu-Mg-Ag heat-resistant alloy were studied by tensile test, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The results show that with the increase of Ag content, the tensile strength and yield strength increase, which is attributed to the increase of the precipitations number and the decrease of the size. The same conclusions are drawn in the study of increasing Mg content. The alloy possesses excellent thermal stability. At 100–150 °C, the strength of the under-aged alloy increases at the initial stage, and after reaching the peak strength, it remains the same. The secondary precipitation of the under-aged alloy occurs in the process of exposure at 150°C, and it distributes diffusely after thermal exposed for 20 h. Then, the tensile strength decreases gradually with increasing the thermal exposure time at 200–250 °C. The strength of the peak-aged alloy decreases gradually, and the precipitation grows up, but the number decreases gradually with prolonging the exposure time at 100–250 °C. The strength of two kinds of alloys decreases with elevating of exposure temperature.

Influence of spraying parameters on cold gas spraying of iron aluminide intermetallics

Cold spraying was used to build up coatings of ordered Fe40Al intermetallics, which are a kind of alloys which are being proposed for high temperature applications. The spray experiments were performed with chemically ordered powder feedstock of different size distributions to study influences from impact velocities. Stainless steel and Ti grade 1 substrates were used to investigate influences of the mechanical and physical properties of the substrate material. While coatings on stainless steel are mostly dense with good cohesion, those on titanium show some cracks perpendicular to the coating substrate interface. That might be due to the larger difference in the thermal expansion coefficients between the titanium substrate and the iron aluminide. Regarding the influence of spraying parameters, it has been found for both substrate materials, that when spraying the first layers, a uniform almost linear decrease in the coating thickness is observed when increasing the spraying distance. By increasing the number of spray layers, the increase in thickness asymptotically approaches a saturation limit. Thicker coatings were obtained on stainless steel substrates than on Ti substrates.

Microstructure and mechanical properties of Al containing ODS ferritic alloys by VHP and HIP

A new Al containing oxide dispersion strengthened (ODS) ferritic alloy Fe–14Cr–3Al–2W–0·1Ti–0·35Y2O3 (wt-%) (14Cr-ODS) was produced by mechanical alloying, followed by vacuum hot pressing (VHP) at 1100°C for 1 h under 35 MPa, and hot isostatic pressing (HIP) at 1160°C for 3 h under 130 MPa. The microstructure and tensile properties of the two kinds of alloys were investigated. TEM studies indicate that the ODS alloys exhibit the characteristic ferritic structure containing Y–Al–O nanoparticles. Tensile characterisation at room temperature has shown that the tensile strengths of 14Cr-ODS alloy after VHP and HIP are 1312 and 968 MPa respectively. After HIP for 3 h, the 14Cr-ODS alloy has much lower tensile strength. However, the ductility of the 14Cr-ODS alloy after HIP is twice as large as that after VHP. The mechanical properties have close relations with the size of nanoparticles and microstructure of the ODS alloy. The size of the oxide nanoparticles and the grain size of the matrix of the ODS alloy after VHP are smaller than those after HIP.

Research on Cutting Vibration in High-Speed Milling Nickel-Base Superalloy

Nickel-base superalloy GH4169 is a kind of alloy with high intensity, heat-stability and heat-fatigability, so that is often used to aerospace field, but which has poor machinability. The cutting force, plasticity deformation all present their particular characters which causes cutting vibration . The cutting vibration influence the surface roughness, the swing of the cutting force and tool wear. This article discusses the superalloy of GH4169 on the basis of cutting speed, cutting depth and feed per-tooth.

Prediction of Fatigue Life for Light Metals and their Welded Metals

A6N01 (6005C in ISO) base metal is applied for cantilever type fatigue test over 108 cyclic number. Fatigue strength decreases over 107 and after testing, new prediction formula of fatigue life at high cycle regeion which named YENs formula is proposed for light metal and their welded joints. This formula is shown as below. Log (σa/σp) =k Log (Nf-N0)+m σa is stress amplitude, σp is proof stress k is depend on stress concentration factor Nf is fatigue life without residual stress and No is discrepancy due to residual stress. m is material constant. This formula is a hypothesis and it is required to accumulate much more fatigue data for many kind of alloys and their welded joints.

Unusual dry sliding tribological behavior of biomedical ultrafine-grained TiNbZrTaFe composites fabricated by powder metallurgy

Abstract

Barocaloric effect in metamagnetic shape memory alloys

AbstractWe report on calorimetric measurements under hydrostatic pressure in a series of composition related metamagnetic shape memory alloys. We show that metamagnetic shape memory alloys exhibit a barocaloric effect whose magnitude compares well to the magnetocaloric effect exibited by this kind of alloys. While in metamagnetic alloys the magnetocaloric effect is inverse, the barocaloric effect has been found to be conventional. The values obtained for the pressure‐induced entropy changes at moderate pressures are in the range of those reported for giant caloric materials.

Phase transformation kinetics in metastable titanium alloys

We investigated the phase transformation sequence, kinetics, and microstructural evolutions during heating, isothermal treatment, and continuous cooling of the metastable Ti–B19 alloy. On the basis of these results, we summarized the phase transformation characteristics of this kind of alloys, especially the metastable β-Ti alloy. We also analyzed and discussed the possibility of describing the size, morphology, and distribution of precipitates as well as the possibility of and complications in establishing relationships among the chemical composition, microstructure, processing parameters, and properties of the metastable Ti–B19 alloy.

Cavitation erosion of several oxy-fuel sprayed coatings tested in deionized water and artificial seawater

Cavitation damage is a concern for stainless steel and other metals in seawater environments, and new coatings are needed to resist such surface damage in that kind of environment. Consequently, a NiCr alloy coating, a WC–17Co/NiCr composite coating, a Fe-based metallic glass coating, a WC–(W,Cr)2C–Ni cermet coating, and a WC–17Co cermet coating were prepared on metal alloy substrates using high velocity oxy-fuel spraying (HVOF). The microstructure and phase composition of as-sprayed coatings and substrates were analyzed using optical microscopy and X-ray diffraction. Vicker's microindentation hardness was measured as well. The cavitation erosion behavior of the five kinds of HVOF-sprayed coatings and three kinds of alloys (316 stainless steel, TC4 titanium alloy and ZL101 aluminum alloy) in both deionized water and artificial seawater was evaluated according to ASTM standard method G 32-10. The corrosion behavior of the alloys and HVOF-sprayed coatings in artificial seawater was evaluated by potentiodynamic polarization tests to reveal the correlation between corrosion and cavitation behavior. Based on the test results, an analysis of the microstructural damage processes, and the cavitation–corrosion synergism of the coatings, the WC–17Co cermet coating was found to be the most promising coating to prevent metallic substrates from cavitation damage in seawater.

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Nickel alloys are very important in many aerospace applications, especially to manufacture gas turbines and aero engine components, where high strength and temperature resistance are necessary. These kinds of alloys have to be welded with high energy density processes, in order to preserve their high mechanical properties. In this work, CO2laser overlap joints between Inconel 718 sheets of limited thickness in the absence of postweld heat treatment were made. The main application of this kind of joint is the manufacturing of a helicopter engine component. In particular the aim was to obtain a specific cross section geometry, necessary to overcome the mechanical stresses found in these working conditions without failure. Static and dynamic tests were performed to assess the welds and the parent material fatigue life behaviour. Furthermore, the life trend was identified. This research pointed out that a full joint shape control is possible by choosing proper welding parameters and that the laser beam process allows the maintenance of high tensile strength and ductility of Inconel 718 but caused many liquation microcracks in the heat affected zone (HAZ). In spite of these microcracks, the fatigue behaviour of the overlap welds complies with the technical specifications required by the application.