形变诱发马氏体对304不锈钢在活化状态下电化学行为的影响

用电化学方法研究了形变诱发马氏体对３０４不锈钢在活化状态下电化学行为的影响．结果表明，随着变形量的增加，马氏体转变量也增加，材料的电化学活性增大；通过测量各单相的电化学行为发现：马氏体的腐蚀电位比奥氏体的约负５５ｍＶ，这是形变诱发马氏体容易被选择性溶解的主要原因．

EOEG装置第四效蒸发器C534上下封头环焊缝及拼缝裂纹原因分析

某石化公司EOEG装置第四效蒸发器C534,在2021年大修检验过程中,于上下封头的环焊缝及拼缝周边发现内表面裂纹。笔者通过渗透检测、硬度检测、铁素体含量检测、金相检测,对奥氏体不锈钢上下封头的环焊缝及拼接焊缝周边产生裂纹原因进行分析,结果显示:由于上下封头的直边段材质是奥氏体不锈钢,在冷加工过程中,部分组织转变成形变马氏体;在氯化物及拉应力作用下,导致上下封头的环焊缝及拼接焊缝周边发生应力腐蚀开裂。提出以下建议:压力容器的制造过程中,应根据不同材质、规格及环境工况,确定合适的加工处理工艺。

Microstructure and martensitic transformation in quaternary NiTiHfV alloy

The effect of age hardening on the microstructure,martensitic transformation behavior,and shape memory properties of the(Ni_(50)Ti_(30)Hf_(20))_(95)V_(5)alloy was investigated by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,differential scanning calorimetry,microhardness,and bending tests.The results demonstrate a significant influence of V addition on the microstructure of the alloy.V addition leads to the formation of a(Ni,V)_(2)(Ti,Hf)-type Laves phase,which coexists with B19'martensite at room temperature.Aging at 550℃results in precipitation hardening due to the formation of nano-scale orthorhombic H-phase,with the peak hardness observed after 3 h of aging.The alloy at peak hardness state exhibits higher transformation strain and lower unrecovered strain compared to the solution-treated sample.The aged sample achieves a maximum transformation strain of 1.56%under 500 MPa.

形状记忆合金式锚杆的提出及抗拔承载力特性分析

针对暴雨、洪水、地震等自然灾害频繁发生而诱发的边坡失稳问题,提出宜用于快速抢险救灾工作的形状记忆合金式锚杆结构,详细阐述其结构组成和技术原理;简化出该结构的抗拔承载力计算模型,基于土体柱孔扩张理论得到扩孔压力和内边界位移关系,基于SMA宏观唯象本构模型,由逆悬臂梁问题的思路求解合金片的扩张力和位移关系,基于合金片与土体的变形协调条件对计算模型进行求解,进而得到锚杆抗拔承载力的计算公式,并依托MATLAB软件编制求解程序;结合算例,使用COMSOL Multiphysics多物理场仿真平台建立有限元模型,对合金片-土体相互作用的力学特性进行仿真分析,结果所得的接触力与理论方法计算的扩张力总体分布趋势相似,验证结构的快锚效果和合金片扩张力理论计算方法的可靠性。算例分析表明:合金片的扩张力主要在其弯曲段增长,合金片厚度越大锚杆抗拔承载力越大;相比传统注浆锚杆,新型锚杆很大程度上缩减了锚固段长度,降低了工程成本。研究成果能够为新型锚杆的设计应用提供理论依据和指导。

Ni_(56)Mn_(25-x)Cr_xGa_(19)(x=0,2,4,6) high temperature shape memory alloys

The microstructure,martensitic transformation behavior,mechanical and shape memory properties of Ni56Mn25-xCrxGa19（x=0,2,4,6） alloys were investigated.Single phase of martensite with tetragonal structure is present for x=0,and dual-phase containing martensite and γ phase is observed for x≥2.The martensitic transformation peak temperatures decrease monotonically from 401 ℃ for x=0 to 197 ℃ for x=6.The introduction of γ phase by Cr addition is proved to be effective in improving the workability and ductility.The tensile stress and strain are 497 MPa and 8 % for x=4,and 454 MPa and 5.5 % for x=6,respectively.The shape memory strain values are 2.7 % under a residual strain of 4.5 % for x=4,and 1.9 % under a residual strain of 3.5 % for x=6,respectively.

Influence of Ni_4Ti_3 precipitates on phase transformation of NiTi shape memory alloy

Ni Ti shape memory alloy samples were aged for 2 h at 573, 723 and 873 K, respectively. Two R-phase variants are observed in the Ni Ti samples aged at 573 and 723 K, where the orientation relationship between the two R-phase variants and the B2 matrix is determined. In the Ni Ti samples aged at 573 and 723 K, fine and homogeneous Ni4Ti3 precipitates are coherent with the B2 austenite matrix. The Ni4Ti3 particles precipitate in the grain interior and at the grain boundaries, where the heterogeneous Ni4Ti3 precipitates are coherent, semi-coherent and incoherent with the B2 matrix in the Ni Ti sample aged at 873 K. As for the Ni Ti sample aged at 873 K, one-stage phase transformation from B19＇ martensite to B2 austenite occurs on heating, but two-stage phase transformation of B2-R-B19＇ arises on cooling. The Ni Ti sample aged at 723 K shows two-stage phase transformation of B2-R-B19＇ on cooling as well, but exhibits two-stage phase transformation of B19＇-R-B2 on heating. The Ni Ti sample aged at 573 K exhibits three-stage transformation on cooling due to local stress inhomogeneity and local composition inhomogeneity around the Ni4Ti3 precipitates.

Antiphase boundary-like structure in α′′ martensite of TC21 titanium alloy

The morphology and formation mechanism of the substructure of martensite in TC21 alloy was investigated by XRD and TEM. The results showed that the martensitic transformation from β to α＂ occurs upon quenching after solution treatment between 960-1000 ℃. The antiphase boundary （APB）-like structure was observed clearly in the α＂ martensite plates. The APB-like contrasts exist along the （001） and （020） planes of α＂ martensite. This APB-like structure of α＂ martensite was identified as a kind of stacking fault with an APB-like morphology induced by martensitic transformation and not by order/disorder transition. During martensitic transformation, martensitic domains nucleate and grow, eventually encounter each other, resulting in the formation of the APBdike contrast.

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.

Influence of cooling rate on phase transformation and microstructure of Ti-50.9%Ni shape memory alloy

Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.

Microstructure and transformation behavior of Ni_(54)Mn_(25)Ga_(15)Al_6 high-temperature shape memory alloy

The microstructure, martensitic transformation behavior, mechanical properties and shape memory effect of Ni54Mn25Ga15Al6 high-temperature shape memory alloy were investigated. By comparing with the Ni54Mn25Ga21 alloy, the effect of Al addition on the properties of Ni-Mn-Ga alloys was analyzed. The results show that the Ni54Mn25Ga15Al6 alloy has a single-phase tetragonal non-modulated martensite structure with lamellar twins. The martensitic transformation start temperature of this alloy is up to 190 ℃, displaying the promising application as a high-temperature shape memory alloy. Al addition in Ni-Mn-Ga alloy can decrease the martensitic transformation temperatures due to the effect of size factor and improve the strength and plasticity. However, the shape memory effect is reduced remarkably with the Al addition.

Magnetocaloric effect in Ni-Mn-In-Co microwires prepared by Taylor-Ulitovsky method

Ni-Mn-In-Co microwires with diameter of 30-100 μm are prepared by glass-coated metal filaments（Taylor–Ulitovsky） method. The effects of magnetic field on martensite transformation temperature in the as-prepared and annealed microwires are investigated using a physical property measurement system（PPMS）. Magnetocaloric effect（MCE） attributed to field-induced austenite transformation in the as-prepared and annealed microwires is analyzed indirectly from the isothermal magnetization（M-B） curves. The as-prepared microwire has a 7-layer modulated martensite structure（7M） at room temperature. The changes of austenite starting temperature induced by an external magnetic field（ΔAs/ΔB） in the as-prepared and annealed microwires are-1.6 and-4 K/T, respectively. Inverse martensite to austenite transformation exists in annealed microwires when an external magnetic field is applied at temperatures near As. The entropy change（ΔS） obtained in the annealed microwires is 3.0 J/（kg·K）, which is much larger than that in the as-prepared microwires 0.5 J/（kg·K）. The large entropy change and low price make Ni-Mn-In-Co microwires a potential working material in magnetic refrigeration.

乙烯装置氢-甲烷分离器上封头开裂泄漏原因分析

某石化公司乙烯装置1号氢-甲烷分离器D30304上封头保温圈支撑板上方母材发生纵向开裂,被迫切出装置临时停工检修。通过现场裂纹宏观观察、渗透检测、硬度检测、铁素体检测、金相组织分析、断口分析及能谱分析,对其亚稳态奥氏体不锈钢上封头开裂原因进行分析,结果表明:奥氏体不锈钢封头冷加工成型过程中产生形变马氏体,低温临氢工况促使大量马氏体组织形成,在应力作用下导致封头不锈钢产生氢致开裂。提出以下建议:根据使用的工况确定合适的加工工艺;对于低温临氢环境下使用的冷冲压成型的奥氏体不锈钢设备,必须进行固溶化处理。

Modeling of Ni_4Ti_3 precipitation during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys

The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initial Ni-contents of 51.5% and 52.5% （mole fraction）, respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni （i.e., Ti-51.5%Ni）, the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni （i.e., Ti-52.5%Ni）, the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.

管道系统中Ti-Ni合金管接头的疲劳寿命(S-N)分析

采用了全寿命(S-N)的有限元分析方法,分析了循环振动载荷下的Ti-Ni合金管接头,给出了有限元计算的疲劳寿命分布图。结果表明,管接头中间内表面处为疲劳寿命的薄弱位置;马氏体相变和逆相变在同一位置的反复发生,是造成局部疲劳损伤/疲劳寿命低的直接原因和起源。

Effect of Sn substitution and heat treatment on microstructure and microhardness of Co_(38)Ni_(34)Al_(28-x)Sn_x magnetic shape memory alloys

Sn was used to replace Al in Co38Ni34Al28 alloy. The microstructure and microhardness of Co38Ni34Al28-xSnx （x=0, 1, 2, 3） magnetic shape memory alloys were investigated at different heat treatment temperatures （1373 K, 1473 K, and 1573 K） for 2 h. The results show that more Sn substitution reduces the content of γ-phase and a partial phase of martensite can be obtained in Co38Ni34Al28-xSnx （x=1, 2, 3） alloys after treatment at 1573 K for 2 h. The maximum martensite phase appears when 2% Al is substituted by Sn. The reverse martensitic transformation temperature of Co38Ni34Al28-xSnx alloys increases at x=1 and 2, then decreases as x=3. As the content of Sn and the temperature increase, the microhardness will increase.

Effect of annealing temperature on martensitic transformation of Ti_(49.2)Ni_(50.8) alloy processed by equal channel angular pressing

The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing （ECAP） was investigated by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）. The as-ECAP processed and subsequently annealed Ti49.2Ni50.8 alloys consist of B2 parent phase, Ti4Ni2O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400℃, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 ℃, the samples show B19′→B2 single-stage transformation. The B2-R transformation is characterized by wide interval due to the dislocations introduced during ECAP.

Effects of solution-aging treatment on microstructures and properties of Ti-55.06%Ni-0.3%Cr alloy

The effects of solution-aging treatment on the microstructures, mechanical properties and internal friction of Ti- 55.06%Ni-0.3%Cr （mole fraction） alloy were investigated by means of tensile test, dynamic mechanical analysis （DMA） and spherical aberration electron microscopy （SAEM）. The results show that the aged alloys with Cr3Ni2 phase always exhibit higher tensile strength and hardness than those of solution-treated alloy without Cr3Ni2 phase, and the aging peak temperature presents at 375 ℃. It is also found that the internal friction peak （tan 6） value decreases with increasing the frequency. There are two internal friction peaks corresponding to the B2（austenite）→R and R→M（martensite） transformations upon cooling, but only one corresponding to the reverse M→B2 transformation upon heating in both solution-treated and 375 ℃-aged alloys, due to the superposition of Mand R phase transformation. Besides, the position of internal friction peaks in the alloy after aging at 375 ℃ shifts to higher temperature. This is attributed to the decrease of Cr and Ni content, and the decline of lattice deformation and transformation resistance, all of which are related to the precipitation of Cr3Ni2 phase in the solution-aged alloys.

Effects of Co and Al addition on martensitic transformation and microstructure in ZrCu-based shape memory alloys

The effect of ternary alloying element Al and quaternary alloying element Co on the martensitic transformation of ZrCu-based shape memory alloy was investigated. The results show that the addition of Al and Co in ZrCu alloy decreases both the martensitic transformation temperature and the martensitic transformation temperature hysteresis. Transmission electron microscope (TEM) observations reveal that theCm martensite structure is the preferential formation phase. The intervariant structures in ZrCuAlCo alloy are (021) type I twins, while the dominant substructures inside the martensite variant are the (001) compound twins. With the increase of Co content, tensile fracture strength and strain are improved obviously.

Microstructural evolution during hot and cold deformation of Ti-36Nb-2Ta-3Zr-0.35O alloy

The Ti-36Nb-2Ta-3Zr-0.350 （mass fraction, %） （TNTZO） alloy was produced by cold isostatic pressing and sintering from elemental powders, followed by hot and cold deformation. The effects of deformation process on microstructures and mechanical properties were investigated using the SEM, TEM, OM and the universal material testing machine. Results show that the alloy can be easily hot forged and cold swaged due to the fine-grained microstructure. Only after cold swaging by 85%, the alloy shows the typical ＂marble-like＂ structure. And thecold deformation is accompanied by stress-induced a＂ phase transformations. Moreover, both the strength and the ductility of the alloy are significantly improved by hot and cold working.

Mechanically-induced martensite transformation of NiTiFe shape memory alloy subjected to plane strain compression

Based on the channel die compression, NiTiFe shape memory alloy(SMA) was subjected to plane strain compression. Mechanically-induced martensite transformation, nanocrystalline and amorphous phase can be observed in the case of large plastic strain. Mechanically-induced martensite transformation is obviously different from the conventional stress-induced martensite transformation. The former generally occurs after dislocation slip, whereas the latter arises prior to dislocation slip. The occurrence of B19’ martensite phase contributes to accommodating subsequent plastic deformation of NiTiFe SMA. Mechanically-induced B19’ martensite is partially stabilized due to the existence of local high stress field and consequently it is unable to be reverted to B2 austenite phase during unloading.