Mechanical and chemical properties of Ni3Si and Ni3(Si,Ti) alloys multiphased by chromium addition

Abstract

The alloying behaviour and microstructure of Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys were first characterised by optical microscopy, X-ray diffraction, and scanning electron microscopy with electron probe analysis. The microstructures of the Ni–Si–Cr ternary alloys consisted of large dispersed Ni₅Si₂ phase and finely precipitated Ni₃Si phase in nickel solid solution, while the Ni–Si–Ti–Cr quaternary alloys consisted of finely precipitated Ni₃(Si,Ti) phase and nickel solid solution. Then, the high temperature mechanical properties, bend strength, and oxidation and corrosion properties of the alloys were investigated. The Ni–Si–Cr ternary alloys showed significant strengthening over a wide range of temperatures, and also large compressive plastic deformation at high temperatures. The strength and fracture toughness at ambient temperatures were correlated with the volume fraction of Ni₅Si₂ phase. The Ni–Si–Ti–Cr quaternary alloys did not show increased yield strength, but exhibited improved tensile ductility and plasticity over a wide range of temperatures. Both Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed substantially improved oxidation resistance in air at 1173 K, compared with Ni₃Si and Ni₃(Si,Ti) alloys. Also, the Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed corrosion resistance comparable to that of the Ni₃Si and Ni₃(Si,Ti) alloys.     

Microstructure and martensitic transformation and mechanical properties of cast Ni rich NiTiCo shape memory alloys

Abstract

The influence of Co additions on the microstructure, second phase precipitates, phase transformation and mechanical properties of cast Ni_51?xTi₄₉Co_x (x?=?0, 0·5, 1·5 and 4 at-%) shape memory alloys was investigated. At the expense of Ni, Co added to NiTi alloy significantly increases the martensitic transformation temperature. The matrix phase in the microstructure of Ni₅₁Ti₄₉Co₀ alloy is the austenite phase (B2) in addition to martensite phase (B19′) and precipitates of NiTi intermetallic compounds. However, the parent phase in the other three alloys, Ni_50·5Ti₄₉Co_0·5, Ni_49·5Ti₄₉Co_1·5 and Ni₄₇Ti₄₉Co₄, is martensite. Ti₂Ni phase was found in the microstructures of the all investigated alloys; however, Ni₃Ti₂ phase precipitated only in the NiTi alloy with 0 at-%Co. The volume fraction of Ti₂Ni phase decreased by the additions of 0·5 and 1·5 at-%Co, while it is slightly increased with 4 at-%Co. The hardness value of NiTi alloy is affected by Co additions.     

Laser-induced combustion synthesis of Zr–Ti–Al–Ni amorphous-based alloys

Bulk metallic glasses, like many crystalline intermetallics, have large negative enthalpy of mixing among the major constituent elements, and hence are potential candidates of self-propagating high-temperature reaction systems. Based on this characteristic, the laser-induced combustion synthesis (LCS) technique has been applied to fabricate amorphous-containing alloys. In the present paper, we report the LCS of the Zr–Ti–Al–Ni alloys. A series of Zr–Ti–Al–Ni alloys is designed and synthesized by LCS. The LCS products mainly consist of intermetallic phases, but in Zr₅₅Ti_10.8Al_17.1Ni_17.1 and Zr₅₀Ti_21.6Al_14.2Ni_14.2 amorphous phases are found. The hardness and tribology characteristics are closely related to the phase contents. The amorphous phases, ductile and soft, lower the hardness and increase the friction coefficient of the LCS samples.     

Internal friction and shear modulus of Ti32Zr18Ni50 hydrogen storage alloy

Abstract

Internal friction and shear modulus measurements were carried out in a Ti₃₂Zr₁₈Ni₅₀ alloy to study the effect of martensitic transformation on hydrogenation properties. The temperatures of martensitic transformation and austenitic transformation weredetermined. The results were compared to those obtained by electrical resistivity and differential scanning calorimetry techniques. The experiments showed two peaks of internal friction, one associated withdislocation relaxations and the other with phase transformations. The microstructurecharacterisation was carried out by scanning electron microscopy. The phase (Ti, Zr)₂Ni was found mainly precipitated in grain boundaries. Some experiments were carried out in specimens with previous plastic strain and another set of samples was tested in a hydrogen atmosphere.With increasing plastic strain, the amplitude of the peak associated with dislocations decreased. Hydrogen addition during the testsled to an increase in the temperature of maximum internal friction.     

Precipitation of second phases in aged Ni rich NiTiRe shape memory alloy

Abstract

This study investigated the effect of aging on the structure and precipitation of second phases of Ni₅₂Ti_47·7Re_0·3 shape memory alloys. The alloy was solutionised at 1000°C for 24 h before aging at various temperatures ranging from 300 to 600°C for 3 h. The matrix phase in both solutionised and aged specimens was martensite. Ti₂Ni phase was also present in the microstructure of both solutionised and aged specimens and its volume fraction decreased as the aging temperature increased. Ni₄Ti₃ phase began in appearance by increasing aging temperature to 400°C. Ni₄Ti₃ precipitates had lenticular and non-geometry shapes. Aging at 600°C led to precipitation of Ni₃Ti phase in the microstructure. This precipitated phase formed in white blocky shapes. Ti/Ni ratio increased and/or Ni content decreased in the matrix with increasing in aging temperature.     

Preparation of NixTiy compound via Ni plating followed by thermal treatment of Ti powder

In this research, Ni_xTi_y compound was prepared by thermal treatment of Ni-plated Ti powder. For this purpose, Ti powder was plated in an electroless Ni bath for various times (120, 225, 300, and 720?min). Hydrazine hydrate was used as a reductant for the deposition of pure Ni on the Ti particles. The plated powder (225?min) was heat treated under argon atmosphere to achieve Ni_xTi_y powder. Finally, the heated/plated powder was pressed by CIP followed by sintering at 980°C for prepare the Ni_xTi_y bulk sample. The plated powders as well as sintered one were characterized using scanning electron microscopy, energy dispersive spectrometer, X-ray fluorescence, X-ray diffraction and differential scanning calorimetric. The NiTi₂, NiTi, and Ni₃Ti phases were detected in the XRD patterns of heated/plated Ti powder. According to DSC data, the heated/plated Ti powder showed reversible martensitic transformation at temperature range of ?38.0°C to +38.1°C, while sintered/heated/plated Ti powder displayed reversible transformation at temperature range of 16.0°C–15.4°C.     

High‐Temperature Shape Memory Effect in Ti‐Ta Thin Films Sputter Deposited at Room Temperature

Ti‐Ta based alloys are potential high‐temperature shape memory materials with operation temperatures above 100 °C. In this study, the room temperature fabrication of Ti‐Ta thin films showing a reversible martensitic transformation and a high temperature shape memory effect above 200 °C is reported. In contrast to other shape memory thin films, no further heat treatment is necessary to obtain the functional properties. A disordered α″ martensite (orthorhombic) phase is formed in the as‐deposited co‐sputtered Ti₇₀Ta₃₀, Ti₆₈Ta₃₂ and Ti₆₇Ta₃₃ films, independent of the substrate. A Ti₇₀Ta₃₀ free‐standing film shows a reversible martensitic transformation, as confirmed by temperature–dependent XRD measurements during thermal cycling between 125 °C to 275 °C. Furthermore, a one‐way shape memory effect is qualitatively confirmed in this film. The observed properties of the Ti‐Ta thin films make them promising for applications on polymer substrates and especially in microsystem technologies.     

Martensitic transformation behaviors of Ti-rich Ti–Ni alloy fibers fabricated by melt overflow

Ti₅₀Ni₅₀, Ti_50.5Ni_49.5, Ti₅₁Ni₄₉ and Ti_51.5Ni_48.5 fibers were fabricated by melt overflow process. The rapid solidification can increase the solubility above the equilibrium solubility. The effects of the rapid solidification of Ti-rich Ti–Ni alloys on the microstructure, transformation temperatures and shape memory characteristics are investigated. The addition of 0.5 at.% Ti in Ti₅₀Ni₅₀ alloy greatly increases the transformation temperature. However, the transformation temperatures decrease again for Ti content exceeding 51 at.%. Results of thermal cycling tests under various constant stress levels reveal that the recoverable elongation associated with B2–B19 martensitic transformation of Ti_50.5Ni_49.5 fibers is two times larger than that of Ti_51.5Ni_48.5 alloy fiber.     

Microstructure and martensitic transformation of Ti49Ni51 − xHfx high temperature shape memory alloys

In present work, the microstructure and martensitic transformation of Ti₄₉Ni_51 − xHf_x (x = 3-15) alloys were studied. The microstructure of Ti₄₉Ni_51 − xHf_x alloys consists of B19′ martensite and (Ti,Hf)₂Ni phase at room temperature. The martensitic transformation behavior is characterized by a single-stage transformation. With increasing Hf content, the transformation temperature increases from 75 to 279 °C resulting from the reduced valence electron concentration, indicating that the replacement of Hf for Ni is effective in increasing the transformation temperatures. The results suggest that the Ti₄₉Ni_51 − xHf_x shape memory alloy is one of potential candidates for high temperature applications.     

Phase transformation and microstructure and mechanical properties of as cast NiTiRe shape memory alloys

Abstract

The microstructure, martensitic transformation and mechanical properties of as cast Ni₅₂Ti_48?xRe_x shape memory alloys (SMAs) were investigated. The microstructure of these alloys consists of B19′ martensite phase as a matrix and B2 austenite in small percentages in addition to some precipitations of NiTi intermetallic compounds. There are two types of NiTi precipitates: the first one is Ti₂Ni, which can be seen in the all microstructures of the three alloys, and the other is Ni₂Ti, which is found only in the microstructure of Ni₅₂Ti_47·7Re_0·3 alloy. According to differential scanning calorimetry measurements, one stage of transformation reaction B2 to B19′ accompanied with forward and backward martensitic transformation was observed. The martensitic peak and the austenitic peak were increased with the addition of rhenium. Both are increased as the number of valence electron per atom increase and the valence electron concentration decrease. Hardness measurements of Ni₅₂Ti_48?xRe_x SMAs are improved by the Re additions.     

A study on martensitic transformation in Ti50−x/2Ni50−x/2Cu x alloys with X≤10 at%

The effect of Cu additions on the martensitic transformation sequence and temperature in Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–10 at% are investigated by ER, DSC, X-ray and IF measurements. Experimental results show that the transformation sequence of Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–4 at% proceeding as two-stage B2RB19 transformation on cooling and Ti_50–x/2Ni_50–x/2Cu _x alloys with x=5, 10 at% have no martensitic transformation. The addition of Cu in Ti_50–x/2Ni_50–x/2Cu _x alloys assists the formation of R-phase, a behaviour which is quite different from that in Ti₅₀Ni_50–x Cu _x alloys. Both the Ms and T _R temperatures decrease rapidly with increasing Cu addition in Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–4 at%. It is proposed that the Cu+Ni effects on the Ms temperature in Ti_50–x/2Ni_50–x/2Cu _x alloys is similar as Cu +Ni effects in Ti₅₀Ni_50–x Cu _x alloys and as Ni effects in as-quenched Ni-rich TiNi alloys.     

Microstructure and tensile properties of Ni3 (Si,Ti) alloys containing second phase dispersions

Abstract

The alloying behaviour, microstructure, and high temperature mechanical properties of quaternary polycrystalline Ni₃ (Si,Ti), which was alloyed with transition elements V, Nb, Zr, and Hf beyond their maximum solubility limits, were investigated. The solubility limits of the quaternary elements in the L1₂ Ni₃ (Si,Ti) phase were determined to be ranked in the sequence of Nb > V > Hf > Zr, and correlated with the size misfit parameter between Si and the quaternary element X, and with the difference in formation enthalpy between Ni₃ Si and Ni₃ X. The second phases (dispersions) formed beyond the solubility limit were identified as a face centred cubic type Ni solid solution for the V containing Ni₃ (Si,Ti) alloy and Ni₃ X type compounds of the Nb, Zr, and Hf containing Ni₃ (Si,Ti) alloys. The second phase dispersions in the L1₂ phase matrix resulted in strengthening over a wide range of temperatures. The high temperature tensile elongation was improved by the introduction of the second phase dispersions. Among the quaternary Ni₃ (Si,Ti) alloys observed in the present study, the Nb containing Ni₃ (Si,Ti) alloy with the Nb containing second phase dispersion was shown to have the most favourable mechanical properties.     

Experimental determination of nickel-rich corner of Ni–Al–Ta phase diagram

Abstract

Liquid–solid and solid–state phase equilibria have been studied in the Ni–NiAl–Ni₃Ta triangle of the Ni–AI–Ta system, using a combination of several experimental techniques. Five primary phases occur in this region, including the ternary compound, π, Ni₆TaAI, which enters into equilibrium with each of the other four. Another compound, Ni₈Ta, forms in the solid state by decomposition of Ta–rich Ni solid–solutions and occurs in equilibrium with the γ, π, and δ (Ni₃ Ta) phases. The extent of these different phase fields has been determined at 1250°C and particular attention has been paid to the γ-γ′ solvus surface which has been shown to be accurately described by a second–order polynomial function of the atomic concentrations.

MST/321     

Phase formation in Ti/Ni dissimilar welds

We explore phase formation in Ti/Ni dissimilar welds using a combination of microscopy and composition analysis (TEM, SEM and EDS). Main microstructural features are NiTi dendrites and Ti₂Ni grains in the inter-dendritic space. The high temperature B2 phase of NiTi is found to transform to trigonal ‘R’-phase, B19^′martensite, and rhombohedral Ni₄Ti₃ phase; these different transformation products highlight the composition inhomogeneity in the parent B2 phase and probable non-equilibrium solidification events during rapid cooling of the weld. Solidification sequence of NiTi and Ti₂Ni was found to vary depending on local conditions in the weld. Formation of impurity nitride phases of titanium is observed which signify incomplete shielding during welding.     

The effects of Co and Ti additions on microstructures and compressive strength of Udimet710

The effects of Co and Ti additions on the microstructures and compressive strength of the Ni-based superalloy Udiemt710 (U710) were investigated. The preliminary results showed that the Ni₃Ti-type (η) phase was observed in the alloys with low Co and Ti content; while a (Ni_xCo_1?x)₃Ti phase with a hexagonal structure was detected in the alloys with high Co and Ti content. The γ′ → η → (Ni_xCo_1?x)₃Ti phase transformation was discussed in terms of Co and Ti contents. The γ′ morphology changed from spherical to cuboidal with increasing Co and Ti content. Compressive tests showed that the alloys with Co and Ti addition possessed higher yield strength than the base alloy, U710. The strength increase could be ascribed to solid–solution strengthening of the γ and γ′ phases as a result of the Co and Ti additions, and the higher volume fraction of γ′ in the new alloys.     

Interfacial reactions between SnAg1.0Ti and Ni metallization

The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this work. Based on the experimental results the following statements can be made: Firstly, the presence of Ti does not have measurable effects on the thickness evolution of Ni₃Sn₄ during solid state annealing. Secondly, the results from long term heat treatments show that there is no marked solubility of Ti to Ni₃Sn₄. Rather Ti reacts with Sn to form large Ti₂Sn₃ platelets inside the solder matrix. The Sn-rich part of the Ni–Sn–Ti phase diagram was assessed in order to rationalize the experimental results. By utilizing this information, the absence of any marked effects of Ti on the growth of Ni–Sn intermetallic compounds (IMC) was analysed. As there is no solubility of Ti to SnAg solder or to Ni–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Ni–Sn IMC layer thickness or quality by Ti alloying.     

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.     

Investigation of Ti(Zr–Ni) Hydrogen-Sorbing Alloys as Electrode Materials for Nickel–Metal-Hydride Storage Batteries

We studied cyclic charge–discharge characteristics of partially substituted and oxygen-containing derivatives of a Ti₂Ni alloy by using specially designed equipment based on PI-50-1 potentiostats and a computer. For Ti_3.8Zr_0.2Ni₂O _x alloys, a twofold increase in the discharge capacity was detected as the oxygen content increased from x = 0 to x = 0.3. It was established that the effect of the hydrogenation–desorption–disproportionation–recombination process on the homogeneity of the Ti4Ni2O_0.3 alloy and its electrochemical charge–discharge parameters in alkaline electrolytes is positive.     

Role of alloying elements in microstructures of beta titanium alloys with carbon additions

Abstract

The effect of 0.2 wt-%C on the microstructure of beta titanium alloys Ti-15X(Fe, Cr, Mn, Mo, Ni, Co, Cu, and V) has been studied using scanning and transmission electron microscopy. It has been found that coarse eutectic TiC_x tends to be formed in beta titanium alloys containing Fe, Cr, Mo, and Mn, and relatively finer homogeneous TiC_x is formed in alloys containing V, Ta, Co, Ni, or Cu. The volume fraction of TiC_x in alloys containing Cu, Co, and Ni is much less than that in other beta titanium alloys. The oxygen content of the matrix is lower than that of Ti₂C in Cr or alloys containing Mn and higher than that of Ti₂C in alloys containing Mo or Ni. These observations are discussed in terms of the role of phase diagrams and the effect of atomic radius of alloying elements on the dimension of interstitial sites in the host alloy and the sublattice of TiC_x.     

The study of constitutional phases in a Ni47Ti44Nb9 shape memory alloy

The constitutional phases and microstructure of Ni₄₇Ti₄₄Nb₉ alloy have been studied by means of optical microscopy, electron probe X-ray microanalyses (EPMA) and X-ray diffraction. It has been shown that the microstructure of the experimental alloy consists of three phases:TiNi matrix, niobium-rich phase and Ti₃(Ni,Nb)₂ compound. The Nb-rich phase is determined to be β -Nb with bcc structure containing a small amount of Ni and Ti. The β -Nb is a soft phase which forms a eutectic structure with TiNi phase during solidification. After hot working the soft β -Nb phase is dispersed in TiNi matrix and gives rise to a wide transformation hysteresis in the alloy. The Ti3(Ni,Nb)₂ is a harder and embrittlemental phase.