外场辅助定向能量沉积钛合金研究进展

钛合金具有高强度、低密度与高断裂韧性等优异性能,已经广泛应用于航空航天、汽车工程与生物医学等领域。传统钛合金零件制造方法是通过铸造及后续机械加工的方式来获得最终产品,但传统方法难以加工结构复杂的钛合金零件,造成了材料的大量浪费。定向能量沉积为制造钛合金零件提供了一种更有效的加工路径,但该工艺仍然存在着若干问题,如粗大柱状晶、各种缺陷以及力学性能各向异性等。为改善上述问题,外场辅助被引入钛合金的定向能量沉积工艺中。本文主要介绍当前几种主流的外场(形变场、声场、磁场),总结和评述了外场辅助对定向能量沉积钛合金微观组织和力学性能的影响,并对外场辅助定向能量沉积钛合金的发展趋势进行展望。

镍铁镓多晶合金弹热效应的循环稳定性研究

弹热制冷是一种新型固态制冷技术,具有对环境友好和能量利用效率高等优点,有望替代传统的蒸气压缩制冷技术。实现弹热制冷应用的关键在于获得兼具大弹热效应和高循环稳定性的弹热材料作为制冷剂。Ni-Fe-Ga记忆合金是一种很有潜力的弹热材料。该合金采用常规熔炼方法易形成γ相,然而有关γ相对合金弹热性能的影响却缺乏系统和深入的研究。有鉴于此,制备了一种含γ相的Ni_(53.6)Fe_(19.3)Ga_(27.1)多晶合金,采用X射线衍射仪、透射电子显微镜、差示扫描量热仪、电子万能材料试验机以及自制的弹热效应测试系统,分析了其显微组织、力学性能和弹热性能。结果表明,Ni_(53.6)Fe_(19.3)Ga_(27.1)多晶合金的基体是β相,γ相同时分布于晶粒内和晶界上,这种两相结构有助于合金获得大且稳定的弹热效应,室温绝热温变值超过-5 K。

材料科学与工程专业留学研究生教学质量提高途径研究

在全球经济一体化和教育国际化的推动下,来华留学研究生的规模不断扩大,各高校对教学质量愈加重视。文章分析了材料科学与工程专业留学研究生的教育现状,并从课程设置、教学内容、实践教学、师资队伍与教材建设以及教学质量评价体系方面对教学质量提高途径进行了探索。

《功能材料》课程教学方法思考

传统材料产业结构升级与相关高技术的迅猛发展对《功能材料》课程的设置与教学提出了更高的要求。《功能材料》课程具有涵盖面广、内容多、知识更新快的特点,可以从课程的教学内容、教学手段与方式和考核方式方面进行探讨,目的在于提高教学质量与效果,培养具有宽广研究视野与扎实专业知识的创新型人才。

时效对TiNiCr形状记忆合金马氏体相变与超弹性的影响(英文)

通过X射线衍射分析(XRD)、透射电子显微观察(TEM)、差式扫描量热分析(DSC)与拉伸实验研究时效处理对Ti48.4Ni51.1Cr0.5合金显微组织、马氏体相变与超弹性的影响规律与机制。经400°C时效处理30 min后,合金中形成Ti3Ni4析出相。当时效温度介于400°C和500°C之间时,合金表现出两步马氏体相变。经时效处理的Ti48.4Ni51.1Cr0.5合金在室温下表现出优异的超弹性。随时效温度自300°C升高到450°C,超弹性恢复率增加。继续升高时效温度,恢复率下降。超弹性应力滞后表现出相反的变化趋势。通过分析Ti3Ni4析出相随时效处理的演化规律解释了时效处理与马氏体相变和超弹性之间的关系。

“材料科学基础”课程教学内容优化和教学方法的探讨

从《材料科学基础》课程性质和内容出发,围绕教学内容优化、教学方法与教学手段进行了改革与探索。通过对课程内容遴选优化,并引入材料科学前沿知识和基于项目的课堂教学模式,采用多媒体现代化教学手段与传统板书相结合,改进实践教学方法,提高学生自主学习的能力和综合素质。

NiMnGa铁磁性形状记忆合金颗粒／树脂智能复合材料的研究进展

介绍了NiMnGa铁磁性形状记忆合金颗粒/树脂智能复合材料的制备、温度场和磁场响应特性以及阻尼性能的最新研究进展。与NiMnGa多晶材料相比,NiMnGa铁磁性形状记忆合金颗粒/树脂智能复合材料具有很好的加工成型性能,克服了NiMnGa多晶材料的脆性,同时表现出良好的温度场响应特性和阻尼性能,是一种很有发展前景的新型驱动器材料和阻尼材料。在磁场响应方面,新型铁磁性形状记忆合金(NiCoMnIn、NiCoMnSb、NiCoMnGa)/树脂智能复合材料将是未来研究的重点。

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.

Ni-Mn基磁性形状记忆合金第二相的形成及其对相变和性能的影响

Ni-Mn基磁性形状记忆合金具有良好的温度场和磁场诱发的形状记忆效应、超弹性、磁热效应、磁阻效应、弹热效应、交换偏置效应等功能特性。作为一种新型多功能材料,有望应用于驱动器、传感器等多个工程领域。本文详细阐述了包含第二相的Ni-Mn基磁性形状记忆合金的研究现状,梳理和总结了第二相的形成及其对马氏体相变、功能特性和力学性能的影响,提出了一些有待解决的问题,如第二相对包括磁性形状记忆效应在内的磁功能特性的影响,并指出未来应着重于研究第二相形成与演化过程的热力学/动力学因素,对第二相进行合理调控,从而优化合金功能特性。

Preparation and shape memory properties of TiO_2/PLCL biodegradable polymer nanocomposites

The preparation of TiO2/poly（L-lactide-co-ε-caprolactone）（PLCL） nanocomposites and their properties were reported.TiO2nanoparticles were surface modified by ring-opening polymerization of ε-caprolactone（ε-CL）.The resulting poly（ε-caprolactone）-grafted TiO2（g-TiO2） was characterized by Fourier transform infrared spectroscopy（FTIR）,thermogravimetric analysis（TGA） and transmission electron microscopy（TEM）.The g-TiO2can be uniformly dispersed in chloroform and the g-TiO2/PLCL nanocomposites were successfully fabricated through solvent-casting method.The effects of the content of g-TiO2nanoparticles on tensile properties and shape memory properties were investigated.A significant improvement in the tensile properties of the 5% g-TiO2/PLCL mass fraction nanocomposite is obtained：an increase of 113% in the tensile strength and an increase of 11% in the elongation at break over pure PLCL polymer.The g-TiO2/PLCL nanocomposites with a certain amount of g-TiO2content have better shape memory properties than pure PLCL polymer.The g-TiO2nanoparticles play an additional physical crosslinks which are contributed to improvement of the shape memory properties.

Cu-Al-Nb高温记忆合金显微组织与马氏体相变

研究了Cu72Al26.5Nb1.5高温记忆合金马微观组织结构与马氏体相变行为。结果表明,Cu72Al26.5Nb1.5合金的铸态显微组织由基体相、γ2相、Nb(Cu、Al)以及Nb(Cu、Al)2相组成,冷却速度越快,γ2相越少;而Nb(Cu、Al)与Nb(Cu、Al)2相并未随冷却速度变化而发生明显改变。Cu72Al26.5Nb1.5合金在加热冷却过程中发生β1→β1马氏体正逆相变。母相为D03有序的BCC结构,马氏体为M18R堆垛有序单斜结构,马氏体变体多呈自协作形态,变体内部亚结构主要为(1210)孪晶。时效对试验合金相变温度影响较大,在马氏体状态下时效,呈现出较强的马氏体稳定化现象,逆相变温度随时效时间的延长而显著升高。在母相状态下时效,马氏体相变温度随时效时间的延长先下降后上升,最后趋于稳定;在时效初期,逆相变温度随时效时间的延长而增大,在时效后期,逆相变温度随时效时间延长基本不发生变化。

High strength and high electrical conductivity CuMg alloy prepared by cryorolling

The microstructure, mechanical properties and electrical conductivity of the room-temperature and cryogenically rolled Cu-0.2wt.%Mg alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD), hardness measurement, tensile tests and electrical conductivity measurement. The results show that for the cryorolled sample, the grain size is decreased by 41% compared with the sample processed at room temperature. With increasing thickness reduction, the microhardness of the alloy continuously increases and the electrical conductivity decreases. For the sample with 90% thickness reduction rolled at cryogenic temperature, the tensile strength and the electrical conductivity are 726 MPa and 74.5% IACS, respectively. The improved tensile strength can be mainly attributed to the grain boundaries strengthening and dislocation strengthening.

Preparation and characterization of porous NiTi alloys synthesized by microwave sintering using Mg space holder

To obtain the lightweight,high strength,and high damping capacity porous NiTi alloys,the microwave sintering coupled with the Mg space holder technique was employed to prepare the porous NiTi alloys.The microstructure,mechanical properties,phase transformation behavior,superelasticity,and damping capacity of the porous NiTi alloys were investigated.The results show that the porous NiTi alloys are mainly composed of the B2 NiTi phase with a few B19'NiTi phase as the sintering temperature is lower than or equal to 900℃.With increasing the sintering temperature,the porosities of the porous NiTi alloys gradually decrease and the compressive strength increases first,reaching the maximum value at 900℃,and then decreases.With increasing the Mg content from 1 wt.%to 7 wt.%,the porosities of the porous NiTi alloys increase from 37.8%to 47.1%,while the compressive strength decreases from 2058 to 1146 MPa.Compared with the NH4HCO3 space holder,the phase transformation behavior of the porous NiTi alloys prepared with Mg space holder changes,and all of the compressive strength,superelasticity,shape memory effect and damping capacity are greatly improved.

Effect of thermal treatment and ball milling on microstructure and phase transformation of Ni-Mn-Ga-Nb alloys

To clarify phase transformation evolution of Nb-doped Ni-Mn-Ga bulk alloys after aging and ball milling, the microstructure and phase transformation of the aged and ball-milled dual-phase Nb-doped Ni-Mn-Ga alloys were investigated by SEM, EDS, XRD, DSC and susceptibility measurements. The as-cast alloys were mainly composed of the second phase with layer-shape and presented a reduced martensitic transformation with increasing the second phase content. The second phase transformed from layer-shape to dense bar-shape and the martensitic transformation was enhanced after being quenched at 1173 K. After aging at 673 and 873 K, the 3% Nb alloy with less second phase exhibited a single-step phase transformation, whereas the 6% Nb and 9% Nb alloys with more second phase exhibited a two-step martensitic transformation and Curie transition. The martensitic transformation and Curie transition of the as-milled dual-phase particles disappeared and were retrieved after annealing at 1073 K due to the recovery of high ordered structure of the matrix.

Microstructure,phase transformation and mechanical properties of NiMnGa particles/Cu composites fabricated by SPS

Microstructure,phase transformation and mechanical properties of NiMnGa particles/Cu composites prepared by spark plasma sintering method were investigated by SEM,EDS,XRD,susceptibility measurements and mechanical tests.The NiMnGa particles were found to react with Cu matrix and the composites exhibited a similar crystal structure to the Cu matrix.The martensitic transformation and Curie transition of the composites were weakened due to the composition change of NiMnGa particles caused by reactions.With increasing NiMnGa particles content,the martensitic transformation and Curie transition of the composites were enhanced to some extent.However,the martensitic transformation temperature and Curie transition temperature were decreased by~50 K as compared to those of the original NiMnGa particles.The compressive strength of the composites increased with the increase of NiMnGa particles content,whereas the compressive strain was decreased gradually.

Effect of electropulsing on anisotropy in strength of laser metal deposited Ti-6Al-4V alloy

The effect of electropulsing treatment on microstructure and mechanical strength of laser metal deposited Ti−6Al−4V alloy was investigated in order to eliminate the anisotropy in strength of laser metal deposited Ti−6Al−4V alloy by tensile tests,optical microscopy,scanning electron microscopy,electron back-scattered diffraction analyses and transmission electron microscopy.With increasing applied voltages from 0 to 130 V,the evolution of microstructure within columnarβgrains followed the sequence ofα′martensite→colonyαstructure→basket-weaveαstructure.The electropulsing treated at 130 V weakened the texture of martensite withinβgrains.The as-built Ti−6Al−4V alloy showed an anisotropy in yield strength(6.2%).After processing at 130 V,the anisotropy in yield strength was reduced to 0.6%,which was attributed to the almost equivalent distribution of Schmid factor in the samples deformed along different orientations.

NiTi基轴承合金研究进展

高Ni含量的NiTi基合金凭借其高硬度、低弹性模量、耐蚀性能以及无磁性等特点而成为一类重要的轴承合金。全面阐述了国内外在NiTi基轴承合金研究方面的进展,主要包括微观组织、力学性能、摩擦磨损特性与耐腐蚀特性等,重点介绍了热处理工艺、合金元素对合金性能的影响,探讨了NiTi基轴承合金今后的研究重点。

Ni_(43)Co_7Mn_(41)Sn_9高温形状记忆合金薄带的结构和相变

采用单辊快淬法制备了名义成分为Ni_(43)Co_7Mn_(41)Sn_9的高温形状记忆合金薄带,并对其微观组织结构和马氏体相变进行了研究.结果表明,薄带发生一步热弹性马氏体相变,经高温热处理后马氏体相变温度达到160℃.制备态薄带的晶粒为微米级,大小不一,介于2—18μm之间,与块体母合金相比晶粒明显细化,且大部分晶粒沿垂直薄带表面方向生长.室温下,薄带(消除内应力后)为正方结构的非调制马氏体,马氏体变体内部由孪晶亚结构组成.热处理后薄带的相变温度有所下降,但随着热处理温度的升高基本保持不变.

科教融合理念下研究生课程研讨式教学模式改革与实践

科教融合理念已成为现代高等教育的核心理念,对于推动世界一流大学、一流学科建设,推进高水平大学发展具有重要意义。在研究生培养过程中,将科研与教学相结合,引导学生发现新知识、探索新知识、创造新知识,培养学生的创新思维,对加强学生的自主学习能力、科研能力和创新能力培养,对提升研究生人才培养质量具有重要作用。在科教融合理念下,如何改革、提高研究生课程教学水平,如何充分发挥创新型人才培养的关键作用,已成为加强人才培养、建设高水平大学需要关注的重要问题。该文以研究生学位课“纳米材料学”为例,对科教融合理念下开展课堂研讨式教学改革的若干问题进行了研究和探索。

NiCoMnSn高温形状记忆合金的马氏体相变与显微组织

采用差示扫描量热分析（DSC）、光学显微镜、x射线衍射分析（XRD）、扫描电子显微分析（SEM）、压缩试验和物性测量系统（PPMS），系统研究了Ni50-xCoxMn41Sn9（x=0，1，3，5，7，9，10，12，14）合金的马氏体相变、微观结构、相组成、力学性能和磁性能。结果表明，Co含量≥10％时，Ni50-xCoxMn41Sn9合金中析出多呈枝节状的第二相。第二相为富Co贫Sn相，属于面心立方结构，多在晶界上析出，其体积分数随Co含量的增加而增多，热处理不能消除第二相。Co的加入不改变合金的相变顺序，即所有成分合金均发生一步马氏体相变和逆相变，但会导致相变温度下降，当Co含量由0增加到10％（原子分数），马氏体相变开始温度（M8）从196．9℃降低到144．8℃，这是因为Co取代M使得合金基体的价电子浓度下降导致的。Co加入NiMnSn后，提高了合金的力学性能，特别是当合金中存在第二相时，合金的断裂强度和断裂应变量呈现跳跃性增长，两者分别提高了600MPa和7％，主要原因是晶粒细化。磁学测试结果表明，随着co含量的增加，合金磁性有所增强，室温下Co含量为12％的合金表现出典型的铁磁性特征，饱和磁化强度高达118A·m2·kg-1。