SLM制备径向梯度多孔钛/钽及其表征研究

利用增材制造技术制作仿天然骨的径向梯度多孔钛/钽骨科植入物具有广阔的前景。基于三周期极小曲面（triply minimal surfaces,TPMS）建模法建立了平均孔隙率为70%的圆柱型径向梯度孔隙结构,孔隙率由中轴线（90%）向圆周面（30%）逐渐降低。利用激光选区熔化(Selected Laser Melting, SLM)工艺制作径向梯度多孔钛/钽。光学显微镜,扫描电镜,Micro-CT检测结果共同显示,SLM径向梯度多孔钛/钽的孔隙结构与设计特征一致。SLM工艺制作的径向梯度多孔钛/钽的孔隙率分别为73.18%与68.18%。力学测试结果表明,梯度多孔钛/钽的弹性模量分别为3.96±0.19GPa与3.47±0.25GPa,抗压强度分别为90.83±3.35MPa与93.27±1.24MPa。梯度多孔钛/钽的弹性模量与抗压强度分别显著高于均匀多孔钛/钽（孔隙率为70.11%的均匀多孔钛弹性模量为2.34±0.48GPa,抗压强度为67.63±1.33MPa,孔隙率为65.39%的均匀多孔钽弹性模量为1.69±0.49GPa,抗压强度为68.56±0.41MPa）。体外细胞相容性实验证明,径向梯度多孔钛/钽均具有良好的生物相容性,适合间充质干细胞与肌肉细胞的粘附生长。SLM工艺制作的径向梯度多孔钛/钽比均匀多孔钛/钽具有与天然骨组织更相近的结构与性能,是理想的骨缺损修复替代物。     

SLM制备径向梯度多孔钛/钽的力学性能及生物相容性

利用增材制造技术制作仿天然骨的径向梯度多孔钛/钽骨科植入物具有广阔的前景。基于三周期极小曲面(triply minimal surfaces, TPMS)建模法建立了平均孔隙率为70%的圆柱型径向梯度孔隙结构,孔隙率由中轴线(90%)向圆周面(30%)逐渐降低。利用激光选区熔化(selected laser melting, SLM)工艺制作径向梯度多孔钛/钽。光学显微镜,扫描电镜,Micro-CT检测结果共同显示,SLM径向梯度多孔钛/钽的孔隙结构与设计特征一致。SLM工艺制作的径向梯度多孔钛/钽的孔隙率分别为73.18%与68.18%。力学测试结果表明,梯度多孔钛/钽的弹性模量分别为(3.96±0.20)与(3.47±0.25) GPa,抗压强度分别为(90.83±3.35)与(93.27±1.24) MPa。梯度多孔钛/钽的弹性模量与抗压强度分别显著高于均匀多孔钛/钽(孔隙率为70.11%的均匀多孔钛弹性模量为(2.34±0.48)GPa,抗压强度为(67.63±1.33)MPa,孔隙率为65.39%的均匀多孔钽弹性模量为(1.69±0.50) GPa,抗压强度为(68.56±0.41) MPa)。体外细胞相容性实验证明,径向梯度多孔钛/钽均具有良好的生物相容性,适合间充质干细胞与肌肉细胞的粘附生长。SLM工艺制作的径向梯度多孔钛/钽比均匀多孔钛/钽具有与天然骨组织更相近的结构与性能,是理想的骨缺损修复替代物。     

不同孔径分布多孔钛的力学性能

从生物学角度出发设计并制备2种不同孔径分布的多孔钛,并研究其力学性能。采用造孔剂烧结方法制备孔隙率为36%~63%的多孔钛,通过室温压缩测试其力学性能。多孔钛的弹性模量和抗压强度分别在2.662~18 GPa和94.05~468.57 MPa范围内,且都随着孔隙率的增加而降低。抗压强度和孔隙率的关系曲线呈现完全的线性特征,表明抗压强度主要受孔隙率的影响,几乎不受孔径的影响。Gibson-Ashby力学关系分析结果显示：常数项C值的差异说明孔径分布对多孔钛的屈服强度有一定的影响;密度指数n值均大于临界值3,表明这2种不同孔径的多孔钛的变形方式相同,为孔壁的屈曲作用。     

基于TPMS结构的多孔钛制备与表征

多孔钛因具有与人体骨组织相近的弹性模量和允许骨长入的孔隙结构而备受关注。其孔隙结构特征不仅影响骨长入效果,而且决定了多孔钛的力学性能。通过三周期极小曲面(triply periodic minimal surfaces,TPMS)隐函数参数的精确调控可以构建出理想的孔隙结构模型。本实验针对TPMS模型中常用的G单元模型,研究了G单元模型隐函数参数对孔隙率、孔径、杆径等孔隙结构特征的影响规律,设计出了孔隙率约为77%,孔径分别为300(G300)、500(G500)微米的均质孔隙结构;模仿自然长骨径向梯度结构模型,构建了相应的G单元仿生梯度孔隙结构。采用选区激光熔化(SLM)增材制造技术制备了相应的多孔钛样件,利用数字显微镜和扫描电镜观测多孔钛的孔隙结构特征,发现SLM多孔钛实测孔隙率低于设计孔隙率,实测孔径小于设计值,实测杆径大于设计值。力学性能检测结果显示,G300和G500多孔钛弹性模量分别为2.04和3.12GPa,其最大抗压强度分别为63.5和103.5MPa,梯度孔隙结构多孔钛弹性模量和最大抗压强度分别为6.3 GPa和186.9 MPa。研究结果表明,G单元梯度孔隙结构多孔钛是一种理想的承重部位骨缺损修复体。     

以NH_4HCO_3为造孔剂制备的多孔钛及其力学性能

以NH_4HCO_3为造孔剂,采用粉末冶金法在10-3 Pa的真空度下成功烧结出力学性能与骨匹配的多孔钛。利用扫描电镜观察孔的结构,采用X射线衍射仪分析物相组成,利用阿基米德浮水法测定开孔隙率,利用万能材料试验机测量力学性能。结果表明,多孔钛烧结体的主要相为α-Ti,随着造孔剂添加量的改变,并没有出现新相;多孔钛烧结体的开孔隙率范围在6.9%~65.7%之间,且开孔隙率越大平均孔径也越大;抗压强度随开孔隙率的增大而降低,在50~1 558 MPa之间;当造孔剂含量在30%~50%时,所得制品弹性模量在4.1~9.4GPa,理论上很接近人骨的弹性模量(2.3~20GPa)。     

生物医用多孔钛的力学性能及孔结构变形行为（英文）

多孔钛材料因其优良的综合性能被视为最有潜力的生物医用材料之一。考虑到生物材料在使用过程中必然受到力的作用,重点研究了多孔钛的力学性能及其孔结构变形行为。采用添加造孔剂的粉末烧结方法制备孔隙率为36%~66%、平均孔径为230μm的多孔钛。采用扫描电镜观察孔结构形貌,通过室温压缩测试检测力学性能。多孔钛的弹性模量和抗压强度分别为1.86~14.7 GPa和85.16~461.94 MPa,具力学性能与人骨的力学性能相近。建立了多孔钛的相对屈服强度和相对密度间关系,结果表明相对密度是影响多孔钛力学性能和变形的主要因素。对于低相对密度的多孔钛而言,其变形方式为孔壁的屈服、弯曲和屈曲;而对于高相对密度的多孔钛,其变形方式主要为孔壁的屈服和弯曲。     

Ti-13Nb-13Zr表面多孔梯度合金的制备及性能研究

利用放电等离子烧结（SPS）技术制备了中间致密、表面多孔的Ti-13Nb-13Zr梯度合金,研究了烧结温度（950~1200 ℃）对梯度合金组织演变、界面结合、表面孔隙特征、力学及体外矿化性能的影响。结果表明：随烧结温度的逐步上升,梯度合金中α-Ti相减少,β-Ti相增多,组织逐渐连续均匀分布,晶粒得到细化,中间基体与多孔层界面呈连续过渡且形成良好的冶金结合,表面多孔层孔隙率下降而平均孔径减小;梯度合金抗压强度值随烧结温度升高呈先增大后降低趋势,而弹性模量值变化不大;综合分析,烧结温度为1150 ℃时,制备的表面多孔梯度合金不仅具有良好的力学性能（抗压强度893MPa,弹性模量16GPa）,而且具有适宜的孔隙参数（孔隙率34.7%,平均孔径340.9μm）及优异的类骨磷灰石形成能力与体外矿化性能。     

稀土CeO2增强型多孔钛的制备与性能

孔隙率对多孔钛的成骨性能影响较大,高的孔隙率更有利于骨组织的长入。但随着孔隙率的升高,其力学性能必然会急剧下降。因此,如何在保证多孔钛高孔隙率的前提下提高其力学性能,成为当前势必解决的难题。本研究采用浆料发泡法,通过在钛粉中加入不同含量的氧化铈,制备出高孔隙率的多孔钛。结果表明,多孔钛孔隙呈三维网络状,孔隙率为71.6%～73.5%,孔径主要分布在100～700μm,且孔壁上分布着微米级的微孔。当氧化铈的加入量为0.2%(质量分数,下同)时,多孔钛表现出最优的生物力学相容性,其杨氏模量为2.08GPa,抗压强度为60.19MPa。     

SPS烧结温度对NiTi/表面多孔Ti梯度合金组织和性能的影响

利用放电等离子烧结技术制备NiTi/表面多孔Ti梯度合金,研究不同烧结温度对梯度合金微观组织、表面孔隙特征、力学性能及体外生物活性的影响及机理。结果表明:随着烧结温度的升高,梯度合金组织由NiTi、α-Ti、Ni、Ti_2Ni、Ni_3Ti混合相逐渐转变为单一NiTi和α-Ti相,内外层界面形成良好冶金结合,表面孔隙率和平均孔径呈缓慢减小趋势;同时抗压强度值快速增大而弹性模量值变化不大;1000℃制备的梯度合金不仅具有良好的表面孔隙特征(孔隙率35.8%、平均孔径423μm)、较高的抗压强度(632 MPa)、较低的弹性模量(9 GPa)及优异的超弹性行为(超弹性恢复应变4%),而且体外生物活性显著提高。     

造孔剂法制备新型多孔Ti-Nb-Ta-Mo-Zr合金

以尿素、碳酸氢铵和硬脂酸三种不同的材料作为造孔剂,采用粉末冶金法制备出多孔Ti-Nb-Ta-Mo-Zr合金。比较了相同质量分数不同造孔剂对多孔钛合金的显微形貌、孔隙率、抗压强度和弹性模量的影响。结果表明,加入碳酸氢铵的多孔材料孔隙率为34.38%,大部分孔洞直径小于100μm,平均直径为60~80μm,出现超大孔洞的情况较少;且添加碳酸氢铵的多孔材料成孔均匀,孔洞大多为圆形或近圆形,其抗压强度为130.75MPa,弹性模量为9.562 GPa,与人体骨骼的弹性模量相近。因此确定碳酸氢铵作为多孔Ti-2.1Nb-0.9Ta-14Mo-7Zr合金的造孔剂。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。