Phase transformation behavior of pseudoelastic NiTi shape memory alloys under large strain

Although it is known that the plastic deformation after transformation could stabilize martensite and make the transformation irreversible, there lacks a systematic research on the effect of plasticity on phase transformation behavior of NiTi shape memory alloys (SMAs). Therefore, the present study focuses on this aspect of NiTi SMAs. A series of tensile cycling experiments are performed on a NiTi SMA at room temperature. Attention has been paid to the characteristics of the phase transformation stresses, the residual and recoverable strain and the dissipated and recoverable energy density as functions of deformation cycles and maximum strain amplitude. With the increasing of plastic strain amplitude at the first loading cycle, the stress–strain curves reach a stable state sooner during cycling. It is concluded that a small amount of plastic strain at the first loading cycle is helpful to get good stable mechanical properties.     

W、P含量对Ni-W-P化学镀层硬度和耐磨性的影响

目的使Ni-W-P合金镀层具有最大的硬度和耐磨性,通过试验寻找镀层中的最优W、P含量。方法通过改变化学镀液中钨酸钠的加入量(0~75 g/L)制备出不同W、P含量的Ni-W-P镀层。用扫描电镜和能谱仪分析镀层中W、P的含量,用显微硬度计测试镀层的硬度,用球盘式摩擦磨损试验机测试镀层的摩擦系数和磨损率。对比分析镀层的硬度与镀层中的W、P含量,研究它们之间的内在关系。通过X射线衍射仪对镀层进行物相分析,探索W、P含量与镀层中典型物相之间的关系,进而分析其与镀层硬度和耐磨性的关系。并用同样的方法研究了时效处理条件下镀层化学成分与镀层硬度、耐磨性之间的关系。结果试验条件下,当P的质量分数低至6%左右时,镀态镀层硬度最大,耐磨性最好。镀层经过400℃×1h时效处理后,当P的质量分数为8.5%左右、W的质量分数为7.5%左右时,镀层有最大的硬度和耐磨性。结论镀态下,镀层的硬度主要随P含量的增大而减小,W含量对其影响不大。时效态下,镀层的硬度主要随W含量的增大而增大,P含量对其影响不大。     

Electroless ternary Ni-W-P alloys containing micron size Al2O3 particles

In the present investigation electroless ternary NiWP-Al₂O₃ composite coatings were prepared using an electroless nickel bath. Second phase alumina particles (1 µm) were used to codeposit in the NiWP matrix. Nanocrystalline ternary NiWP alloys and composite coatings were obtained using an alkaline citrate based bath which was operated at pH 9 and temperature at 88 ± 2 °C. Mild steel was used as a substrate material and deposition was carried out for about 4 h to get a coating thickness of 25 ± 3 µm. Metallographic cross-sections were prepared to find out the coating thickness and also the uniform distribution of the aluminum oxide particles in NiWP matrix. Surface analysis carried out on both the coatings using scanning electron microscope (SEM) showed that particle incorporation in ternary NiWP matrix has increased the nodularity of composite coatings compared to fine nodular NiWP deposits. Elemental analysis of energy dispersive X-ray (EDX) results showed that codeposited P and W elements in plain NiWP deposit were 13 and 1.2 wt.%, respectively. There was a decrease in P content from 13 to 10 wt.% with a marginal variation in the incorporated W (1.01 wt.%) due to the codeposition of aluminum oxide particles in NiWP matrix. X-ray diffraction (XRD) studies carried out on as-plated deposits showed that both the deposits are X-ray amorphous with a grain size of around 3 nm. Phase transformation studies carried out on both the coatings showed that composite coatings exhibited better thermal stability compared to plain NiWP deposits. From the XRD studies it was found that metastable phases such as NiP and Ni₅P₂ present in the composite coatings heat treated at major exothermic peak temperature. Annealed composite coatings at various temperatures revealed higher microhardness values compared to plain NiWP deposits.     

磷含量对化学镀Ni-W-P合金热处理晶化及电化学行为的影响

用化学沉积法制备了非晶态和混晶态两种Ni-4.9%W-P合金(P含量为11.26%及5.98%)。通过XRD定量分析技术研究了P含量对镀层退火晶化的影响,获得了晶粒尺寸、晶格应变及晶化程度等显微组织特征。通过极化曲线和交流阻抗测试,并采用SEM对镀层腐蚀前后的形貌观察,分析了镀层的电化学腐蚀行为。不同处理态镀层在0.5 mol H2SO4溶液中的极化测试表明,其腐蚀形式为均匀腐蚀,腐蚀机理主要取决于P含量及热处理晶化获得的显微组织结构;在3.5%NaCl溶液中的EIS测试表明,其腐蚀行为表现为点蚀,腐蚀机理在很大程度上受到镀层缺陷的影响,尤其是镀层中存在的孔洞,孔洞的数量越多,尺寸越大,就越容易发生点蚀。     

加热温度对铝合金化学镀Ni-W-P合金组织及相变行为的影响

通过差示扫描热分析仪(DSC),X射线衍射(XRD),透射电镜(TEM)等测试手段研究了6061铝合金基体化学镀Ni-W-P合金的组织及相转变行为.结果表明,Ni-W-P镀层为微晶结构,直径为（5-6）nm,200℃加热1h后,镀层仍为微晶,但有所长大,直径约为30nm,300℃,400℃,525℃和600℃加热1h后,镀层析出Ni3P和Ni相,没有其它亚稳相析出;400℃时Ni-W-P镀层硬度达到峰值,大约为940HV0.1。     

Kinetics of phase separation in iron-based ternary alloys. I. Theoretical analysis of phase separation behavior in iron-based ternary alloys

Phase sepation behavior in an Fe-based ternary system was investigated by using a model based on the Cahn–Hilliard equation. The asymptotic behavior of the minor element, Y, in an Fe–X–Y ternary alloy along a trajectory of a peak top of the major element, X, is classified into three groups according to the sign of the second derivative of the chemical free energy f₁ with respect to the concentration of X, c_X and the concentration of Y, c_Y, f′_XY≡∂²f₁/∂_CX∂_CY. If f′_XY>0,, the value of c_Y along the trajectory of the peak top of Y decreases with time. When f′_XY<0 at 0t<∞, peaks of c_Y formed at the peak tops of Y. The amplitute of the peak increases with time. In the case that f′_XY<0 at 0t<t₀and f′_XY>0 at t₀<t<∞, peaks of c_Y formed at the peak tops of Y at the initial stage. Bifurcation of peaks occurs. The concentration of the major element, c_X, along the trajectory of its peak increases with time regardless of the sign of f′_XY.     

铝合金化学镀Ni-P、Ni-W-P组织及相转变行为

采用差示扫描热分析仪（DSC）、X射线衍射（XRD）等研究了6061铝合金基体化学镀Ni-P、Ni-W-P合金的组织结构及相转变行为。结果表明，镀态Ni-P、Ni-W-P镀层的结构都是微晶结构；200℃热处理1h后．Ni-P、Ni-W-P镀层仍为微晶，但微晶有所长大；300、400、525和600℃热处理1h后，Ni-P、Ni-W-P镀层析出Ni3P和Ni晶体，没有其它亚稳相析出；400℃时Ni-P、Ni-W-P镀层硬度达到峰值，其值分别为840HV100和940HV100。     

Phase transformation and damping behavior of lightweight porous TiNiCu alloys fabricated by powder metallurgy process

Porous TiNiCu ternary shape memory alloys (SMAs) were successfully fabricated by powder metallurgy method. The microstructure, martensitic transformation behavior, damping performance and mechanical properties of the fabricated alloys were intensively studied. It is found that the apparent density of alloys decreases with increasing the Cu content, the porous Ti₅₀Ni₄₀Cu₁₀ alloy exhibits wide endothermic and exothermic peaks arisen from the hysteresis of martensitic transformations, while the porous Ti₅₀Ni₃₀Cu₂₀ alloy shows much stronger and narrower endothermic and exothermic peaks owing to the B2-B19 transformation taking place easily. Moreover, the porous Ti₅₀Ni₄₀Cu₁₀ alloy shows a lower shape recovery rate than the porous Ti₅₀Ni₅₀ alloy, while the porous Ti₅₀Ni₃₀Cu₂₀ alloy behaves reversely. In addition, the damping capacity (or internal friction, IF) of the porous TiNiCu alloys increases with increasing the Cu content. The porous Ti₅₀Ni₃₀Cu₂₀ alloy has very high equivalent internal friction, with the maximum equivalent internal friction value five times higher than that of the porous Ti₅₀Ni₅₀ alloy.     

铝合金化学镀Ni-P、Ni-W-P组织及相转变行为

采用差示扫描热分析仪(DSC)、X射线衍射(XRD)等研究了6061铝合金基体化学镀Ni-P、Ni-W-P合金的组织结构及相转变行为。结果表明,镀态Ni-P、Ni-W-P镀层的结构都是微晶结构；200℃热处理1h后,Ni-P、Ni-W-P镀层仍为微晶,但微晶有所长大；300、400、525和600℃热处理1h后,Ni-P、Ni-W-P镀层析出Ni_3P和Ni晶体,没有其它亚稳相析出；400℃时Ni-P、Ni-W-P镀层硬度达到峰值,其值分别为840HV100和940HV100。     

Electrochemical behavior of multicomponent amorphous and nanocrystalline Zr-based alloys in different environments

Electrochemical behavior of multicomponent melt spun Zr-based amorphous as well as nanocrystalline alloys have been studied in three different corrosive media (neutral NaCl, basic NaOH and acidic H₂SO₄ solutions). Due to the presence of strong passivating elements, (Zr and Ti) melt spun ternary alloys (Zr₅₅Ti₂₅Ni₂₀) have shown complete passivation in NaCl solution even as they contain a small amount of crystallinity. Amorphous multicomponent alloys containing Cu (Zr₅₈Cu₂₈Al₁₀Ti₄ and Zr₆₅Cu_7.5Al_7.5Ni₁₀Pd₁₀) show active nature in NaCl solution and this is strongly related to selective dissolution of base metal (Zr) and enrichment of Cu in the pit region. In NaOH and H₂SO₄ solutions, all the alloys have shown complete passivation irrespective of the alloy composition.     

Phase field modeling of the tetragonal-to-monoclinic phase transformation in zirconia

The allotropic phase transformation in zirconia from the tetragonal to monoclinic double lattices is known to occur by a martensitic twinning mechanism which shows a complex dependence on temperature, stress and environment. This paper is concerned with the development of a phase field model which accounts for the main metallurgical mechanisms governing this martensitic transition. The symmetry reduction and orientation relationship between the parent and product phases were simulated using several non-conserved order parameters representing different transformation paths. Inhomogeneous and anisotropic elastic properties were considered to determine the resultant elastic stresses. Governing equations of the tetragonal-to-monoclinic transformation were solved in a finite element framework under a variety of initial and boundary conditions. It was shown that applying different initial conditions, such as seed embryo or random, did not change the twinning patterns or the final volume fractions of the parent and product phases after the relaxation period. On the other hand, enforcing different boundary conditions resulted in completely different twinning patterns and phase volume fractions. The model was able to predict both the “V” shape morphology of twinning and the surface stress relief with “gable roof” patterns, which were observed by transmission electron microscopy and atomic force microscopy to be characteristic of the tetragonal-to-monoclinic transition.     

Phase transformation of nanocrystalline anatase powders during high energy planetary ball milling

1　INTRODUCTIONTitaniumdioxideisknowntoexistinthreecrys tallineformsofrutile ,anataseandbrookiteinnature .Rutileisthermodynamicallystablewhileanataseandbrookitecantransformirreversiblyandexothermicallytorutileoverarangeoftemperatures[1] .Inaddition ,therearetwohigh pressurephases ,srilankitewithorthorhombicstructureandTiO2 Ⅲ .Underhighpressure ,anataseandrutilecantransformtosri lankite[2 4 ] .Thesrilankitephasecantransformbacktorutileunderappropriateconditions[5] .Overthepastfew years …     

Ni-P非晶薄膜晶化相与相变动力学的XRD分析

用原位XRD技术分析了连续加热过程中电沉积Ni-P薄膜晶化与相变行为．通过定量分析,确定出不同温度下各相的析出量,由此计算出各相的晶化与相变激活能以及晶化结晶度．结果表明, Ni-P非晶薄膜的晶化与相变行为与薄膜中P的含量有关．在晶化过程中出现了四种亚稳相即NiP,Ni2P,Ni12P5及Ni5P2．计算得到:亚稳相NiP,Ni2P及稳定相Ni3P的相变激活能分别为133±15,172±19及190±20 kJ／mol;单个析出相的相变激活能低于Ni-P合金晶化激活能和Ni原子的自扩散激活能．     

Transformation behavior of shock-compressed Ni48Ti52

The transformation behavior on shock-loaded Ni₄₈Ti₅₂ has been studied by employing a differential scanning calorimeter in order to reveal residual effects of shock treatment in the thermoelastic martensitic transformation of Ni₄₈Ti₅₂, exhibiting a shape memory effect between a high temperature phase and a low temperature phase. The shock treatment of Ni₄₈Ti₅₂ was performed by a flyer plate impact method with the flyer velocity of 1.2 km s⁻¹. The height of the exothermic and endothermic peaks due to the transformation of shock-treated Ni₄₈Ti₅₂ become small and their temperature regions are expanded. Although the increase of the number of the thermal cycles induces no intermediate phase on Ni₄₈Ti₅₂ before the shock treatment to result in a one-step transformation, a three-step transformation is observed after annealing at an appropriate temperature on the shock-treated Ni₄₈Ti₅₂, which correspond to the appearance of two intermediate phases. The shock treatment increases non-chemical free energy such as strain energy and interfacial energy of a phase boundary, which is attributable to the microstructure of shock-induced dislocations and an increase of the disorder in the lattice of ordered Ni₄₈Ti₅₂, resulting in the three-step transformation. Therefore, it is thought that the shock treatment can make it possible to achieve a new state on NiTi.     

The sulfidation behavior of Co-Mo alloys containing various ternary additions

The sulfidation behavior of Co-Mo-X alloys, where X is Al, Cr, Mn, or Ti, has been studied over the temperature range 600 or 700°C to 900°C in 10^–2 atm. sulfur vapor to determine the effectiveness of the various ternary elements at reducing the sulfidation rate relative to Co-Mo alloys. For comparative purposes, each ternary alloy contained a constant atomic proportion (i.e., 55Co, 20Mo, and 25X). All of the alloys were multiphase, and sulfidized to form complex, multilayered scales. The scales usually consisted of an outer layer of cobalt sulfide, an intermediate layer that contained primarily the ternaryelement sulfide, and an inner layer which was heterophasic. Usually, each phase within the multiphase alloy sulfidized independently of one another. In the region of the alloy/scale interface there was often a narrow band of fine porosity (transitional band) together with fine precipitates that separated the inner sulfide from the base alloy. It was found that Al and Cr improved the sulfidation resistance of the Co-Mo binary alloy, whereas Mn had the opposite effect. The Ti-containing alloy underwent a mixed sulfidation/oxidation process, so that its kinetics were inapplicable. Aluminum was found to exert the most beneficial effect. The sulfidation behavior of Co-Mo-Al alloys containing a range of Al concentrations was studied at both 700 and 900°C. It was found that for Al to be effective, a sufficient amount of the spinel, Al_0.55Mo₂S₄, had to form within the inner portion of the scale.     

Differences of transformation behavior between Ni-rich TiNi shape memory films and alloys

The differences of transformation behavior between Ni-rich TiNi shape memory film (SMF) and shape memory alloy (SMA) age-treated at 773K after solution-treatment at 973K have been investigated, using Ti-51.5Ni thin film and Ti-51.5Ni bulk alloy as examples, by differential scanning calorimetry (DSC), SEM and EDX. It is found that the age-treated Ni-rich TiNi SMF and SMA are of the same types of transformation, i.e., A→R→M (during cooling), and M→A (during heating) (A: parent phase; R: R-phase; M: martensite); the transformation temperature of the TiNi SMF is lower than that of the SMA, but the SMFs hysteresis is larger. The transformation heat of the TiNi SMF and SMA is nearly the same. The reason that TiNi SMFs strain is sensitive to temperature is not hysteresis, but its thickness is thinner, and the temperature is easy to distribute homogeneously.     

Microstructure, phase transformation and mechanical properties of Ni-Mn-Ga-Y magnetic shape memory alloys

Influence of rare earth Y addition on the microstructure and phase transitions and mechanical properties of polycrystalline Ni₅₀Mn₂₉Ga₂₁ ferromagnetic-shape memory alloy (FSMA) are investigated. It is shown that microstructure of the Ni-Mn-Ga-Y alloys consists of the matrix and the Y-rich phase. The Y-rich phase firstly disperses homogeneously in the matrix with small amounts and then tends to segregate at the grain boundaries with increasing Y substitution for Ga. The Y-rich phase is indexed to Y(Ni,Mn)₄Ga phase with a hexagonal CaCu₅ type structure. The structural transition from 5 M to 7 M, and then to non-modulated T martensite appears with the increase of Y content. The martensitic transformation temperature increases remarkably with increasing Y content, whereas the Curie temperature almost keeps unchanged. It is revealed that the appropriate addition of Y significantly enhances the yield strength and improves the ductility of the alloys. The mechanism on the influence of Y content on the improved mechanical properties and martensitic transformation temperature is also discussed.     

高碳帘线钢的冷却相变行为

利用热模拟机Gleeble-3800测定了高碳帘线钢的动态CCT和TTT曲线,研究了冷却速度和等温转变温度对组织性能的影响。结果表明,连续冷却时,形成晶界渗碳体的临界冷速为1.5℃/s,形成马氏体组织的临界冷速为11℃/s。等温转变时,珠光体转变的温度区间为600～700℃,当温度为625℃时,转变时间最短。等温温度升高,相变时间延长,等温温度降低则会形成贝氏体等异常组织。实际采用斯太尔摩控冷时,将吐丝温度控制为900℃,开启前5台风机,风量分别为100%/100%/80%/50%/30%,保证相变冷速在5～7℃/s,且在相变前尽快通过网状碳化物形成的区间,可以得到组织性能满足技术要求的高强帘线钢。     

Phase transformation and microstructure of NiAl/Ni3Al alloys containing Ti

The effects of titanium additions on A_s temperature, phase transformation behavior and microstructure have been studied in β+γ^′ two-phase alloys. When the endothermic β^′→β transformation appeared first during heating of martensite, a mesh type microstructure, which has no resemblance to the original martensite plates, was obtained.     

Phase transformation of fully lamellar γ-TiAl alloys in α γ field

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