金刚石含量与粒度对自蔓延高温烧结钛铝碳结合剂/金刚石复合材料组织与形貌的影响

采用Ti、Al、石墨和金刚石粉体为原料,通过自蔓延高温烧结制备Ti2AlC结合剂/金刚石复合材料,研究金刚石含量和粒度对该复合材料的物相组成与显微形貌的影响。结果表明,原料粉末发生自蔓延反应,可生成Ti2AlC基体相,同时亦生成TiC和Al_3Ti相。金刚石粒度较细(W5)时,金刚石表面C元素充分地与Ti反应生成TiC,同时基体主相变成TiC和Al,没有Ti_2AlC形成。当金刚石粒度较粗(30/40目)时,基体的主相为Ti_2AlC;金刚石与基体结合紧密。当添加金刚石粒度为120/140目时,基体的主相为Ti_2AlC和TiC。当采用170/200目金刚石为原料时,研究金刚石含量对复合材料基体组成与显微组织的影响时,发现原料中添加10%与20%的金刚石后得到的样品基体的主相为Ti_2AlC、TiC和Al3Ti相与金刚石;金刚石表面均包覆着良好的TiC与Ti_2AlC组织。但是当金刚石含量增加至30%时,基体的主相为TiC,同时含有少量的Ti_2AlC、Ti和Al_3Ti等相;金刚石表面受到一定程度的侵蚀,被一些TiC晶粒所包裹。提出一个Ti-Al-石墨-金刚石体系的自蔓延反应机制,即Ti和Al首先发生化学反应,生成Al_3Ti并放出大量的热,然后,原料中的石墨与金刚石表面转变的石墨都与Ti反应形成TiC,TiC与周围的Ti-Al相不断反应形成Ti2AlC。最后,基体主相为Ti_2AlC,金刚石表面亦形成Ti2AlC。     

电铝热还原电炉钛渣制备Ti-Al-xFe-ySi合金

利用攀枝花产的电炉钛渣铝热还原一步合成Ti-Al-xFe-ySi多元合金,探索CaO对渣金分离、合金收率及钛收率的影响。当CaO/Al=1.1时,制备的熔渣主要生成了低熔点Al_2O_3·CaO和7Al_2O_3·12CaO相,渣金分离效果最好。合金收率达到62%,Ti收率达到92%,合金中氧含量仅为1.32%。制备的合金主要物相为TiAl_3、TiAl相,而渣中还原出来的Fe替代了TiAl3中的部分Ti形成了Al_3Ti_(0.75)Fe_(0.25)物相,而Si主要与合金中的Ti结合生成了Ti5Si3相,合金中还含有少量的碳与TiAl和TiSi相形成了Ti_3SiC_2和Ti_2AlC新相。     

金刚石含量与粒度对钛铝氮结合剂/金刚石复合材料组织的影响

采用Ti、Al、TiN、石墨和金刚石粉体为原料,通过自蔓延高温烧结制备Ti_2AlN结合剂/金刚石复合材料,研究金刚石颗粒的含量和粒度对该复合材料的物相组成与显微形貌的影响。结果表明,原料粉末发生自蔓延反应,生成Ti_2AlN基体相,同时亦生成TiN、Al N和Al3Ti相,金刚石表面生成致密的TiC或Ti_2AlC。当金刚石粒度较粗(30/40,80/100目)时,金刚石表面反应程度较差,形成不连续的TiC与Ti_2AlC组织,基体的主相为Ti_2AlN。当金刚石粒度较细(W20)时,金刚石表面C元素与Ti充分反应生成TiC,基体主相变成TiC和TiN,未形成Ti_2AlN。当金刚石粒度为170/200目时,随金刚石含量增加,金刚石与基体元素的反应程度增加,基体中TiC和Al含量随之增加,而Ti_2AlN含量相应减少。     

元素粉末冶金方法制备TiAl基合金

详细介绍了采用元素粉末冶金方法制备TiAl基合金的机理、工艺方法及材料性能,元素Ti,Al粉末在一定温度下的反应合成主要由扩散控制,包括产生TiAl_3相和TiAl_2相的中间化过程,元素粉末冶金TiAl合金的工艺方法有元素粉末Ti,Al的反应烧结、热压或热等静压,热爆合成,元素TiAl箔片的反应合成等,采用这些方法制备的TiAl基合金具有均匀、细小的组织,但其力学性能受氧含量及孔隙的严重影响。     

元素粉末法制备TiAl基合金

详细综述了采用元素粉末法制备TiAl基合金的机理研究,工艺方法及材料性能。元素里,则在一定温度下的反应合成主要由扩散控制,包括产生TiAl₃相和TiAl₂相的中间化过程。由元素粉末制备TiAl合金的工艺方法有Ti,Al元素粉末的反应烧结、热压或热等静压、热爆合成、元素Ti、Al箔片的反应合成等。采用这些方法制备的TiAl基会金具有均匀、细小的组织,但其力学性能受氧含量及孔隙的严重影响。.     

氢化钛-石油焦制备Al-Ti-C-Ce母合金显微组织及其凝固机制研究

采用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等现代检测分析方法,研究了由TiH_2-石油焦-铝铈合金与铝液制备的不同Ce含量的Al-Ti-C-Ce母合金的显微组织,结果表明:Al-Ti-C-Ce母合金由α(Al),(TiC),(TiAl_3),(Ti_2Al_(20)Ce)相组成; Al-Ti-C-Ce母合金铸样晶界为连续的共晶组织,晶内分布着大量的粗大第二相组织,晶界共晶和晶内第二相中均含有Ti_2Al_(20)Ce相。部分大颗粒第二相组织为复合结构,复合晶粒内部存在颜色较深的α(Al)+Ti_2Al_(20)Ce+(TiC)的包晶组织。线分析结果表明:第二相粒子中,元素C的分布相对均匀,粒子内部C, Al含量相对较低, Ti, Ce含量相对较高, Ce的分布显著高于粒子外部区域;具有复合结构的第二相中所包含的粒子区域, Ti, C含量极高,而Al, Ce含量较低。合金在凝固过程中, TiC粒子作为晶核优先析出, TiAl_3相通过TiC粒子形核,并与游离的Ti, Ce发生包晶反应生成Ti_2Al_(20)Ce相,多余Ce原子会与晶界处的TiC, TiAl_3的复合粒子反应生成TiC, Ti_2Al_(20)Ce复合粒子。含Ti, C, Ce的复合粒子作为领先相优先析出,细化Al-Ti-C-Ce母合金晶粒。     

废SCR钛基脱硝催化剂铝热还原重熔制备含铬钛铝基合金的试验研究

首次利用废选择性催化还原(SCR)脱硝催化剂为原料,采用铝热还原—重熔法进行了Ti-Al基合金制备的试验研究,并通过添加不同含量的Cr元素,研究Cr对合金微观组织、物相组成及性能的影响。通过X射线衍射(XRD)和能谱(EDS)分析,发现未添加Cr元素的合金中所观察到的相主要由Ti_(0.8)V_(0.2)Al_3、TiAl_2、Ti_3Al、TiAl等钛铝金属间化合物,Ti_5Si_3、TiSi_2等钛硅化合物,CaAl_4O_7、Ca_2AlSiO_(5.5)等氧化物组成。添加Cr元素可降低高铝型钛铝化合物的形成,减少钙铝氧化物含量,形成含铬元素的Ti_(0.25)Cr_(0.08)Al_(0.67)相,增加Ti_3Al与TiAl类物相的生成。通过Pandat热化学软件的物相衍变计算得出,Cr的添加可大幅度降低Al_3(Ti,V)的相比率,降低一定量的(Ti,Cr)_5Si_3相比率,同时增加TiAl相的形成。硬度测试结果表明,随Cr含量的增加,合金硬度整体呈上升趋势。这可能是由于等轴晶TiAl类物相的均匀分布和(Ti,W)_5Si_3相的减少所导致的。     

TiC对自蔓延高温合成Ti3AlC2相的影响

以Ti、Al和C粉末为原料的自蔓延高温合成试验研究结果表明:在n(Ti)∶n(Al)∶n(C)=2∶1∶1体系中,未添加TiC时,合成产物中有大量的杂相Ti2AlC生成;当添加≤22.5%(原子数分数)TiC时,合成产物中TiC的含量减少,Ti3AlC2的含量显著增多,Ti2AlC杂质相消失;添加＞22.5%(原子数分...     

Al含量对燃烧合成Ti_3AlC_2的影响

以Ti、Al和C为原料,研究了Ti∶C＝2∶1(摩尔比)时,不同Al含量(27%、33%、38%)对燃烧合成Ti3AlC2的影响.结合热力学原理和Ti-Al-C相图讨论了Al含量对燃烧合成Ti3AlC2的影响机理.结果表明,Al含量对燃烧合成Ti3AlC2的影响较大,产物中的主相都是Ti3AlC2,但杂相不同,即Al含量较低时杂相为TiC;Al含量较高时杂相为Al3Ti,当Al含量为33%时合成的Ti3AlC2的纯度最高.     

Sn掺杂对SHS法制备三元金属陶瓷Ti3AlC2的影响

分别以3Ti/Al/2C/xSn粉末和2Ti/Al/C/0.9TiC/xSn(x=0,0.1,0.2,0.3,0.4,0.5)为原料自蔓延高温合成Ti3AlC2,利用XRD、SEM着重研究了Sn的添加量对产物中Ti3AlC2含量的影响,确定出当产物中Ti3AlC2含量最高时的x值;研究结果表明:添加适量的Sn可消除产物中的Ti2AlC,明显促进Ti3AlC2的合成,并且当x=0.3时,产物中的Ti3AlC2含量最高,比未添加Sn时的含量增加近20％,但Sn的含量继续增加时,Ti3AlC2的含量陡然下降,产物中随之出现大量的Sn,TiC的含量也明显增多;并分析了Sn对合成产物物相组成的影响.     

Ti-xCr-yCu钛基材料的制备及组织性能研究

通过粉末冶金法制备了Ti-xCr、Ti-yCu及Ti-xCr-yCu钛基材料,研究了Cr、Cu含量对其相组成、显微组织、压缩屈服强度、弹性模量以及切削加工性能的影响规律。结果表明:随Cr含量的增加,Ti-xCr钛基材料依次出现了Ti_4Cr、TiCr_2及Cr相,其压缩屈服强度表现出先增大后减小的趋势,当Cr含量为10%时其屈服强度达到最大值(710 MPa),同时,添加Cr元素有利于降低钛基材料的弹性模量,最低可达25 GPa。添加Cu元素的钛基材料,随Cu含量的增加,Ti_2Cu相增加,并且显微组织细化,屈服强度降低;弹性模量受Cu含量影响较小而受烧结温度影响较大。添加Cr和Cu元素的钛基材料,其显微组织主要为网篮组织,弹性模量低于纯钛,其中添加Cu元素有利于细化层片,添加Cr元素有利于细化等轴组织。此外,Cr含量为5%时,钛基材料具有较佳的切削加工性能。     

不同卸载应力对层状TiAl基合金损伤程度的影响

通过对层状TiAl基合金进行拉伸卸载试验，研究了不同预损伤对层状TiAl基合金断裂行为的影响。试验结果表明：随着损伤程度增加到一定程度，材料的弹性模量减小；随着预损伤程度的增加，裂纹面密度增大。通过统计分析发现裂纹面密度可以作为衡量损伤程度的损伤参量；但随着预损伤程度的增加，单位面积断裂功基本不变，进一步说明不同预损伤对层状TiAl基合金的最终断裂性能没有影响。     

Microstructure,Tensile Properties,and Hot-Working Characteristics of a Hot Isostatic-Pressed Powder Metallurgy Superalloy

A series of microstructure observation, tensile, and hot compression tests were conducted to investigate the variation of microstructure, tensile properties, and hot-working characteristics of a powder metallurgy (PM) superalloy with hot isostatic pressing (HIPing) temperature, to establish a basis for the parameter selection for PM superalloy preparation. The results show that the dendritic structure from the powder was not completely removed until the HIPing temperature is above the γ′ solvus; γ/γ′ eutectic formed when the powder particles were HIPed at 1533 K (1260 °C) or above. Prior particle boundaries (PPBs) were observed in alloys HIPed at 1513 K (1240 °C) and below; the PPB decoration is serious in alloys HIPed at 1483 K and 1513 K (1210 °C and 1240 °C), owing to melting and aggregation of the boride phase at the particle boundaries during HIPing; the PPBs were eliminated when the HIPing was done at 1533 K (1260 °C) or above. Tensile fracture mode of the alloy changes from inter-particle and transgranular mixed fracture to transgranular fracture with increasing HIPing temperature, which is in accordance with the change in precipitate distribution at the PPBs. The hot workability of alloy is poor for all combinations of HIPing/deformation conditions except for HIPing at sub-solvus temperature and deformation at low strain rates.

     

Effects of cerium substitution on phase components,microstructures and magnetic properties of Nd-Fe-Ti-B alloy

(Nd_(1-x)Ce_x)_(12)Fe_(77)Ti_5B_6(x = 0,0.2,0.3,0.4,0.6,0.8)alloys were prepared by melt-spinning and annealing techniques.The phase constitutions,microstructures and magnetic properties were investigated by powder X-ray diffraction(XRD),a differential scanning calorimeter(DSC),a vibrating sample magnetometer(VSM)and a transmission electron microscope(TEM).It is found that with the increase of Ce content,the coercivity of the(Nd_(1-x)Ce_x)_(12)Fe_(77)Ti_5B_6 alloys reaches maximum first and then decreases.The maximum coercivity reaches 18.5 kOe obtained in the sample of 20% Ce substituted which is 34%higher than the Ce-free sample.TEM results reveal that the micro structure refinement effect is responsible for the coercivity improvement.This phenomenon implies that in some cases,Ce and Ti co-doping is more beneficial to improving of the coercivity than Ti single doping in Nd-Fe-B alloys.With further Ce addition,magnetic properties deteriorate due to the formation of CeFe_2 and TbCu_7-type phases.     

冷压烧结制备Cu-15%Cr_2AlC复合材料的组织与性能研究

以自制的高纯Cr_2AlC陶瓷粉体为原料,采用冷压真空烧结技术制备了Cu-15%Cr_2AlC(质量分数)复合材料。研究了不同压制压力、烧结温度及烧结时间对复合材料的电阻率、热导率、摩擦因数以及材料的断裂方式和组织结构的影响。结果表明:随着压制压力的增大、烧结温度的升高,复合材料的电阻率、摩擦因数呈下降趋势,热导率逐渐升高;随着烧结时间延长,复合材料的电阻率逐渐降低,摩擦因数先降低后升高,热导率先升高后降低;复合材料的断裂方式均为脆性断裂;随着烧结温度的提高、烧结时间的延长,Cr_2AlC与Cu发生固溶强化效应,引起Cr_2AlC晶格常数畸变。     

Si含量对TiAlSiN纳米复合涂层的微观结构和力学性能的影响

采用不同Si含量的TiAlSi复合靶,在Si基底片上用射频磁控溅射工艺沉积了TiAlSiN纳米复合涂层,采用X射线衍射仪(XRD)、高分辨透射电子显微镜(HRTEM)和纳米压痕技术研究了Si含量对TiAlSiN涂层的微观结构和力学性能的影响.结果表明:TiAlSiN涂层内部形成了Si3N4界面相包裹TiAlN纳米等轴晶粒的纳米复合结构.随着Si含量的增加,TiAlSiN涂层的结晶程度先增加后降低,涂层内部的晶粒尺寸先减小后趋于平稳,涂层的力学性能先升高后降低.当Si与TiAl原子比为3∶22时获得的最高硬度和弹性模量分别为37.1GPa和357.3 GPa.     

Fabrication of aluminum–ceramic skeleton composites based on the Ti<Subscript>2</Subscript>AlC MAX phase by SHS compaction

A one-stage manufacturing technology of aluminum–ceramic skeleton composites by combining the processes of self-propagating high-temperature synthesis (SHS) of a porous skeleton formed by the MAX phase of the Ti₂AlC composition and its impregnation by the aluminum melt under pressure (SHS compaction) is considered. A composition of the exothermic charge 2Ti + C + 22.5 wt % Al + 10 wt % TiH₂, which provides the formation of a porous skeleton of the Ti₂AlC phase without impurity phases by the SHS technology, is selected. It is shown that, when impregnating the hot SHS skeleton with aluminum, new phases are formed such as the MAX phase (Ti₃AlC₂), titanium carbide (TiC), and titanium aluminide (Al₃Ti). However, the content of the basic MAX phase remains high, and the ceramic component of the material consists of Ti₂AlC by 76%. When analyzing the microstructure, it is revealed that the composite has certain residual porosity after impregnation and cooling. The influence of the impregnation pressure (q = 22, 28, and 35 MPa) on the distribution of the aluminum content over the height and radius of the diametral sample section is investigated experimentally. It is shown that the nonuniform Al distribution over the sample bulk is caused by the nonuniform pressure and temperature fields, as well as the different compactibility of hot inner and colder outer sample parts. The degree of compaction of characteristic zones is leveled as the impregnation pressure increases, and the composition inhomogeneity over the sample bulk decreases. The difference in aluminum concentration over the sample bulk at q = 35 MPa does not exceed 5%. The SHS-compacted aluminum–ceramic skeleton composite based on the Ti₂AlC MAX phase corresponds to high-strength Al-Zn–Mg–Cu aluminum alloys by the hardness level (HB ≈ 150 kg/mm²).     

放电等离子烧结制备超细晶钨钛合金

采用放电等离子烧结法制备了Ti原子数分数在15%～30%的钨钛合金，研究了不同Ti含量钨钛合金的相组成、微观结构和超细晶形成机制。结果表明:采用放电等离子烧结技术可在1100 ℃、保温5 min的条件下制备出含β₁(Ti,W)和β₂(Ti,W)两相的钨钛合金，在Ti元素偏聚和快速烧结的共同作用下，厘米级块体样品的晶粒尺寸可达亚微米量级，钨钛合金的性能随Ti含量增多而先增强后降低。当Ti原子数分数为25%时，样品相对密度达（98.5±0.1）%，W晶粒平均尺寸约（340±20）nm，硬度和抗压强度分别达到HV（860±2）和（2600±10）MPa。     

SHS Metallurgy of Cr<Subscript>2</Subscript>AlC MAX Phase-Based Cast Materials

A review of publications on the structure, properties, fabrication methods, and application fields of materials based on the Cr₂AlC MAX phase is given. It is noted that the most promising method of formation of such materials is self-propagating high-temperature synthesis (SHS), one of the directions of which is SHS metallurgy. A powder mixture of chromium III and chromium VI oxides of the analytical grade, aluminum of ASD-1 grade, and carbon is used as the base charge in investigations. The adiabatic combustion temperature and composition of final products is calculated using the THERMO special program. Experiments were performed in an SHS reactor with volume V = 3 dm³ under the initial pressure of inert gas (Ar) P₀ = 5 MPa. The influence of the ratio of initial reagents on SHS parameters (the combustion rate, pressure increment, and yield of the target product), composition, and microstructure of target products is investigated experimentally. A scientific approach of the formation of cast materials in the Cr–Al–C system consisting of the Cr₂AlC MAX phase and phases Cr₃C₂ and Cr₅Al₈ by the SHS metallurgy method is developed. The structural-phase states of target products are studied. It is established experimentally that, varying the content of initial reagents (aluminum and carbon) in the charge, it is possible to substantially affect the synthesis regularities, composition, and microstructure of final products. An increase in the content of the Cr₂AlC MAX phase in the final product and a decrease in the Cr₅Al₈ content occur with an increase in the carbon content (above stoichiometric) in the initial mixture. An increase in the aluminum content (above stoichiometric) in the initial mixture leads to an increase in the content of the Cr₂AlC MAX phase in the final product and a decrease in the content of the Cr₃C₂ phase.     

发动机用石墨烯增强TC11合金放电等离子烧结制备参数优化及力学性能研究

通过添加石墨烯提高了放电等离子烧结（spark plasma sintering, SPS）制备发动机用耐高温TC11合金的力学性能,研究了不同烧结参数下TC11合金的密度,并观察了合金显微组织,分析了合金力学性能的影响因素。研究结果表明:随着烧结温度增加,试样密度先增加后平稳;提高烧结压力后,试样密度发生了略微上升。随着烧结温度的上升,更多α相转变成了高温β相,形成了相对稳定的β相比例。随着烧结时间的增加,合金室温压缩强度表现为升高的趋势。提高烧结压力后,TC11合金获得了更高的室温与高温力学强度。通过实验最终确定烧结时间5 min、温度900 ℃与压力50 MPa时制备的TC11合金具有最优力学性能。