First-principles calculation of structural and thermodynamic properties of titanium boride

The equilibrium lattice parameters, electronic structure, bulk modulus, Debye temperature, heat capacity and Gibbs energy of TiB and TiB2 were investigated using the pseudopotential plane-wave method based on density functional theory (DFT) and the improved quasi-harmonic Debye method. The results show that the total density of states (DOS) of TiB2 is mainly provided by the orbit hybridization of Ti-3d and B-2p states, and the total DOS of TiB is mainly provided by the hybrids bond of Ti-3d and B-2p below the Fermi level and Ti—Ti bond up to the Fermi level. The Ti—B hybrid bond in TiB2 is stronger than that in TiB. Finally, the enthalpy of formation at 0 K, heat capacity and Gibbs free energy of formation at various temperatures were determined. The calculated results are in excellent agreement with the available experimental data.

Titanium effect on the microstructure and properties of laminated high boron steel plates

High-boron steel is an important material used for thermal neutron shielding. The appropriate amount of added boron must be de- termined because excessive boron may deteriorate the steel＇s workability. A uniform microstructure can be formed by adding titanium to boron steel. In this study, casting and hot rolling were used to fabricate laminated high-boron steel plates whose cores contained 2.25wt% boron and 0wt%-7.9wt% titanium. The effects of titanium content and hot-rolling and heat-treatment processes on the microstructure and properties of the laminated plates were studied. The results indicated that the optimum titanium content was 5.7wt% when the boron content was 2.25wt%, and that the best overall properties were obtained after heat treatment at 1100℃ for 4 h. The tensile strength, yield strength, and elongation at the specified temperature and holding time were as high as 526.88 MPa, 219.36 MPa, and 29%, respectively.

TC4表面激光熔覆硬质复合涂层组织与性能

TC4凭借比强度高、耐腐蚀性好、质量轻等一系列优点,被广泛应用于航空航天领域,但其摩擦系数大、耐磨性差等缺点极大地限制了其应用范围,针对TC4硬度低、耐磨性差等缺点,采用4 kW大功率Laser4000半导体激光器,选用过渡族难熔碳化物HfC、TaC和ZrC作为增强相,以H13钢基粉末作为基粉,利用激光熔覆技术在TC4表面制备了不同比例的钢基金属-陶瓷硬质涂层。之后利用扫描电镜(SEM)、EDS能谱仪、D/max-2500/PC型X射线衍射仪(XDR)等试验手段对不同比例涂层的宏观形貌、显微组织、物相组成和涂层元素分布等进行对比分析,利用Qness型号维氏显微硬度计测试涂层硬度并分析熔覆试样截面微观硬度变化规律,利用MMU-5G型端面摩擦磨损试验机研究了不同材料组分涂层的摩擦磨损性能,研究结果表明:试件熔覆层与基材形成了良好的冶金结合,熔覆层组织形态主要以枝晶组织以及块状组织为主,各熔覆层的主要物相中均含有TiC,随着三元陶瓷粉末含量的增加,MC的含量也随之增加,当碳化物混合粉末添加量为15%(质量分数)时,熔覆层中检测到Hf_(0.8)Ta_(0.2)Fe_(2)三元合金相。当三元陶瓷粉添含量为10%(质量分数)时,熔覆层晶粒最为细小,涂层平均硬度最高,平均硬度约为763.43 HV,是基材硬度的2.29倍,当三元陶瓷粉末含量为5%(质量分数)时涂层的耐磨性最好,相对耐磨性为25%。

Microstructure and properties of nano-TiN modified Ti(C,N)-based cermets fabricated by powder injection molding and die pressing

Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.

Investigation of the Boriding Process of the Ti-Al Intermetallic Alloy GE48-2-2 Taking into Account the Probability of the Influence of the Substrate Modification

Boriding of the Ti-Al intermetallic GE48-2-2 at 1273 K for 10 hours was performed. In order to ensure that no any serious alteration occurred in the substrate, it was previously examined with X-Ray Diffractometry (XRD), after it has undergone an annealing process at the temperature of boronizing. Subsequently, we examined the coating with XRD and Scanning Electron Microscopy, in order to characterize its structure and morphology. A dense TiΒ2 layer, 10 - 15 μm thick, was formed, but also Cr2B3 and NbN, BN and some Ti-Al phases were detected. Efforts were undertaken to focus on influence of the substrate modification, towards the quality of the coating.

Effects of pretreatment and HVOF sprayed cermet coating on fatigue properties of TC21 titanium alloy

The effects of grit blasting (GB),shot peening (SP) pretreatment and high velocity oxygen fuel(HVOF) sprayed WC-17Co cermet coating on the fatigue properties of the novel ultra-high strength TC21 titanium alloy were investigated with a rotating bending fatigue test machine.The basic properties and surface integrity of the coating were investigated by using X-ray diffraction (XRD),surface roughness meter,microscopic hardness tester,scanning electron microscopy (SEM) and X-ray stress test instruments.The results showed that the residual compressive stress could be introduced into the surface of TC21 alloy by GB and SP pretreatment,and that HVOF sprayed WC-17Co coating was compactly bonded with TC21 alloy substrate and it significantly improved the surface hardness of the substrate.However,there was a certain residual tensile stress in the sublayer of the coating.SP could significantly increase fatigue resistance of TC21 alloy due to the surface residual compressive stress.There was no significant effect on fatigue resistance by GB treatment due to the offset between the influence of surface residual compressive stress and the surface notch effect.The fatigue resistance of TC21 alloy was significantly reduced by HVOF WC-17Co coating prepared with GB pretreatment.This could be attributed to the relaxation of surface residual compressive stress during the HVOF heating process,pore defects and residual tensile stress distribution in the WC-17Co coating with low toughness,and the surface notch induced by GB.The fatigue resistance of TC21 alloy was slightly reduced by HVOF WC-17Co coating prepared with SP pretreatment.This was attributed to the offset between the advantage effect by SP and disadvantageous effect of WC-17Co coating and high temperature factor during the HVOF process.

Ti(C,N)基金属陶瓷复合材料热压烧结制备与性能研究

采用热压烧结工艺制备了碳氮化钛(Ti(C,N))基金属陶瓷复合材料。利用场发射扫描电镜(SEM)对试样的断口与表面形貌分别进行了观察,对力学性能进行了测试并研究了其抗氧化性能。研究结果表明:试样断口的微观结构形貌组织致密度高,气孔的数量少,晶界分明且晶粒尺寸细小,裂纹的断裂路线走向清晰,凹凸起伏,同时存在穿晶断裂和沿晶断裂方式。力学性能分别为:弯曲强度1255 MPa,断裂韧性8.3 MPa·m^(1/2),维氏硬度11.9 GPa,相对密度98.7%。在设定的温度条件下氧化2 h后,在750℃时没有形成氧化膜层;在900℃时,试样表面形成的氧化膜对基体没有保护效果;而在1150℃时,试样的表面形成了致密的对基体具有保护作用的氧化膜层和中间过渡层,氧化膜层厚度大约为73.81μm,而中间过渡层厚度约为18.57μm。

Structure,tribological properties,and the growth mechanism of in-situ generated TiC in titanium cermet

Titanium cermet combining metallic toughness with ceramic wear resistance has been proven to be a potential candidate for implanted joint material.In this work,titanium cermet was synthesized by means of the elevated temperature solid carburizing technology.The Ti_(13)Nb_(13)Zr alloy surface was found to be converted into TiC ceramic layer combined with a carbon strengthened diffusion zone underneath.The overall thickness of the carburized region grew to about 100 um after 120 min carburization at 1,500 K.In order to clarify the growth behaviors of TiC ceramic layer,a growth mechanism is proposed.At the beginning of carburizing process,carbonaceous gas decomposed from carburizer due to high temperature and then converted to free atomic carbons through reduction reaction.Then,in-situ generated TiC ceramic layer possessing certain thickness formed on the surface,meanwhile,the inner carbon diffusion zone also grew inwards due to physical diffusion of carbon,and finally forming a gradient carbon distribution.In addition,the tribological behaviors of the new materials were evaluated through reciprocating ball-on-plate sliding wear tests in bovine calf serum.Although there was an increase in friction coefficient,the wear rate decreased by 59.6%due to the formation of the wear-resistant TiC ceramic layer.The wear mechanisms evolved from severe abrasive wear for bare Ti_(13)Nb_(13)Zr alloy to mild adhesive wear for titanium cermet.

热压烧结TiB_2-ZrB_2固溶复合陶瓷的结构研究

以ZrB2 作为掺加剂 ,通过热压烧结制备了TiB2 -ZrB2 固溶复合陶瓷。采用X射线衍射分析对材料的相组成、晶格常数和晶体结构进行了分析 ,材料的显微结构分别由EPMA ,SEM和TEM测定。研究结果表明 ,随着ZrB2 掺入量的增大 ,固溶产物的晶格常数会相应增加 ,当ZrB2 的掺加量为 8% (摩尔分数 )时 ,产物的晶格常数出现极大值 ;ZrB2 可以与TiB2 形成部分固溶的固溶体 ,在复合材料中存在富Ti和富Zr的两种硼化物 ;由于固溶反应在界面上进行 ,有效地降低了烧结过程中的晶界移动速度 。

Ti(C,N)基金属陶瓷显微组织的研究

用粉末冶金方法制备了Ｔｉ（Ｃ，Ｎ）基金属陶瓷，其硬度、抗弯强度和断裂韧性分别可达ＨＲａ９１．２ ，１ ２５０ ＭＰａ 和１３ ．４ＭＰａ·ｍ １２ ，ＴＥＭ 研究表明，陶瓷相／ 金属相、陶瓷相／ 陶瓷相界面分别存在一定的取向关系，揭示了液相在烧结后的凝固过程．

镁热还原自蔓延高温合成硼化钛微粉的动力学

应用DTA技术分别测定了Mg与TiO2 ,Mg与B2 O3及Mg与TiO2 和B2 O3之间的多相反应 ,分析了Mg ,TiO2 和B2 O3三相可能存在的反应机制 ,应用Freeman Carroll法和Kissinger法计算了反应的活化能和反应级数。结果表明Mg B2 O3 TiO2 之间的反应为复杂的固液液反应 ,TiO2 与Mg之间的固 液反应放出的强大热量诱发了B2 O3和Mg之间的液液反应 ,而Ti与B间的反应放出的热量反过来又促进前两者的反应。表观活化能在温度段 760～ 85 8℃为E1=2 97kJ·mol-1,相应的反应级数分别为n1=0 .8。采用Kissinger法计算的反应级数为0 .9,与Freeman Carroll法所得的n1=0 .

Ti(C,N)基金属陶瓷的力学性能与显微结构的研究

热压烧结制备了不同Mo2 C和Cr3C2 含量的Ti(C0 .7N0 .3) -(Ni-Co) -Mo2 C -Cr3C2 金属陶瓷 ,对其性能测试表明 ,低Mo2 C ,Cr3C2含量材料具有良好力学性能。利用透射电镜、能谱分析和扫描电镜对低Mo2 C ,Cr3C2 含量金属陶瓷显微组织进行了分析。研究表明 ,材料显微组织中没有发现明显可见的环形相 ,Mo元素富集在硬质相颗粒边缘附近 ,Cr元素富集在粘结相中。未完全溶解的Cr3C2 分布在粘结相内和相界上抑制了裂纹的扩展 ,断口上沿晶断裂面弯曲不规整以及穿晶解理条纹较多 。

Er对Ti(C,N)基金属陶瓷结构和力学性能的影响

研究了添加稀土金属Er对Ti(C ,N)基金属陶瓷结构和力学性能的影响 .结果表明 ,加入稀土金属Er能有效地提高金属陶瓷的硬度、抗弯强度和断裂韧性 .稀土金属Er能改善金属相对陶瓷相的润湿性 ,使气孔率降低 ;此外 ,稀土金属Er在陶瓷相 /金属相、陶瓷相中晶粒界面以及金属相和陶瓷相中形成化合物 ,净化了界面 ,提高了界面结合强度 ,从而改善了力学性能 .

TiCN基梯度功能金属陶瓷的制备及其切削性能

以TiCN-WC-Mo2C-TaC-Co-Ni为原料,通过成分和气氛控制,获得了功能梯度TiCN基金属陶瓷材料。采用带有能谱分析仪的扫描电子显微镜和X射线衍射仪观察和分析了材料的微观组织和物相组成,通过车削实验考察了所制备的刀具的切削性能。结果表明,WC含量较低时,通过气氛控制可以获得表面富Ti层、中间富W层和基体的3层TiCN基金属陶瓷梯度层,烧结温度的提高有利于梯度层的厚度的增加;WC含量较高时,烧结后WC在表面富集。15%WC含量的TiCN基金属陶瓷在1 460℃氮气气氛中烧结1 h时,富Ti层的厚度约为15~20μm,富W层厚度约为15~20μm。经氮化烧结后材料表面的（Ti,W,Mo）（C,N）衍射峰相对材料内部向右偏移。真空烧结时,当WC含量较低时,Ti和W元素分布比较均匀;随着WC含量的升高,表面出现了贫Ti富W层,且随着WC含量增加,表面富W层增厚,WC含量为24%时,富W层厚度〉25μm。切削实验表明表面富Ti的金属陶瓷的切削性能优于表面富W的金属陶瓷材料。

TiB_2系金属陶瓷的SHSQP制备

从理论和试验上对ＴｉＢ２ｘＦｅ复合体系的ＳＨＳ过程参数进行了分析。计算得到ＴｉＢ２４０％Ｆｅ（以摩尔计）的ＳＨＳ过程激活能为３９９ｋＪ／ｍｏｌ，接近Ｔｉ＋２Ｂ在低燃烧温度区域的反应过程激活能，预示着一种扩散控制机理。进行了ＳＨＳＱＰ技术制备密实金属陶瓷的研究，包括加压延迟、压力延续和压力大小等参数对产品密实度的影响。通过优化和控制有关参数，制备出了良好力学性能的金属陶瓷。

硼含量对Ti-50Al-xB合金中TiB_2微观形貌的影响

用 XRD,SEM对原位自生法制备的 Ti- 5 0 Al- x B (at% )合金的相组成和微观组织进行了研究。结果表明 :该合金主要由 Ti Al和 Ti B2 两相组成 ;Ti B2 主要以片状、板片状、细棒状和块状形式存在 ;Ti B2 微观形貌随着合金中B含量的变化而发生显著变化。当 B含量由 0 .4at%增加至 1.4at%时 ,Ti B2 的微观形貌由片状依次演变为板片状、细棒状直至块状 ,而基体形貌没有明显变化。根据 Ti B2 晶体形核与生长条件对 Ti

钛及钛合金渗硼的研究现状与反应机理

钛合金表面渗硼可极大地提高钛合金的耐磨性能.本文综合阐述了国内外钛及其合金表面渗硼的研究现状,探讨了固体渗硼法中表面渗层形成机理与硼钛化合物的生长动力学.基体组织、渗剂组成、渗硼温度、氧分压等因素会影响渗硼层结构.在接近β转变点的温度条件下,可能获得较厚的渗硼层.双相结构中的TiB与TiB2层的厚度d与时间t的关系分别满足Fick扩散第二定律d2=K·t.

TiB/Ti基金属陶瓷的自蔓延高温合成与耐磨性研究

通过自蔓延高温合成结合准热等静压技术制备了TiB/Ti基金属陶瓷 .采用环块接触形式进行材料的耐磨试验 .研究了TiB/Ti基金属陶瓷材料的微观组织和相结构 ,重点探讨了它的磨损特性和磨损机制 .结果表明 :TiB/Ti基金属陶瓷具有优良的耐磨性 ,在干摩擦条件下 ,载荷为 4kg ,磨损时间为 2h时 ,材料几乎没有质量损失 ,其磨损机制主要为粘着磨损。

激光熔覆原位合成TiC-TiB_2/Ni基金属陶瓷涂层的组织和摩擦磨损性能

采用激光熔覆技术,以NiCrBSiC预合金粉末为原料,在TC4合金表面制备出以原位合成的TiC和TiB2颗粒为增强相的Ni基金属陶瓷涂层。测试了涂层的显微硬度。利用销-盘式摩擦磨损试验机,以YG8B硬质合金为对磨偶件(盘),评价了涂层的干滑动摩擦磨损性能。结果表明:涂层的硬度Hv为900～1100,摩擦系数为0.2～0.3,质量磨损率比TC4合金降低约1个数量级。

自蔓延高温合成/快速加压法制备(TiB_2+Fe)/Fe梯度材料

通过对不同Fe含量的Ti+B +Fe体系绝热温度计算和试样温度有限元计算 ,确定了 (TiB2 +Fe) /Fe梯度材料各层合理的厚度 ,并采用SHS/QP技术制备了 (TiB2 +Fe) /Fe梯度材料。电子探针分析表明 (TiB2 +Fe) /Fe梯度试样中各层间没有了明显的界面 ,沿厚度方向由富陶瓷相向富金属相连续转变。背散射电子像分析表明从富陶瓷侧到富金属侧 ,材料的显微结构也是梯度变化的。SEM分析表明 ,从富陶瓷层到富金属层 ,TiB2 晶粒减小。