Thermodynamic analysis of the formation of tetragonal bainite in steels

In the articles of Bkhadeshia, a new class of high-strength steels based on the structure of carbidefree bainite with an enhanced carbon content has been developed. According to Bkhadeshia, the main factor responsible for the high solubility of carbon is the occurrence of a tetragonality of the bainite lattice. To check this effect, in this article, the theory of tetragonality of martensite of iron alloys developed by Zener and Khachaturyan was applied to bainite under the assumption that the precipitation of carbides is prohibited. Equations for the chemical potentials of carbon and iron in austenite and in tetragonal ferrite have been derived. The equilibrium of these phases has been considered, and the calculations of the boundary concentrations of carbon and iron at different temperatures (300–1000 K) and at different parameters of the deformation interaction λ₀ have been performed. The rigorous calculations confirmed Bkhadeshia’s hypothesis that the suppression of the carbide formation during the formation of bainite leads to an increase in the carbon solubility in the bcc phase.     

Thermodynamic Analysis of Burning Resistivity of Ti-Cr-V-Mo Alloys

ＴｈｅｒｍｏｄｙｎａｍｉｃＡｎａｌｙｓｉｓｏｆＢｕｒｎｉｎｇＲｅｓｉｓｔｉｖｉｔｙｏｆＴｉＣｒＶＭｏＡｌｏｙｓ①ＬｉｕＹｕｑｉｎ，ＺｈｕａｎｇＷｅｉｄｏｎｇ，ＢａｉＫｅｗｕ，ＳｈｅｎＪｉａｎｙｕｎ②ａｎｄＺｈａｎｇＺｈｕ（刘玉芹）（庄卫东）（白...     

Thermodynamic modeling of the Ba–Ni–Ti system

The binary Ba–Ni and Ba–Ti systems are modeled by computational thermodynamics using the CALculation of PHAse Diagram (CALPHAD) method, wherein the thermodynamic parameters of disordered bcc, fcc and hcp phases are evaluated in terms of the first-principles calculations using the special quasirandom structures (SQSs). In combination with the Ni–Ti system modeling in the literature, the phase equilibria of the Ba–Ni–Ti system are predicted. Isothermal section of the ternary system is presented.     

Properties of Ti−V and Ti−V−Al alloys with oxygen

Metal Science and Heat Treatment -     

Thermodynamic calculations of carbonitrides in microalloyed steels

A three-phase miscibility gap including the austenite and two carbonitrides is presented to describe the phase equilibria between the austenite matrix and carbonitride precipitates. It is demonstrated that the three-phase equilibrium has a lower Gibbs energy than the conventional two-phase equilibrium of austenite and one carbonitride, and is more consistent with experimental data in the literature.     

On Ti6Al4V Microsegregation in Electron Beam Additive Manufacturing with Multiphase-Field Simulation Coupled with Thermodynamic Data

Electron beam additive manufacturing is an effective method for the fabrication of complex metallic components. With rapid solidification, the characteristics of microsegregation within the interdendritic region are interesting and important for the subsequent phase transformation and final mechanical properties. However, in view of the microsecond lifetime and the small length scale of the molten pool, experimentally investigating microsegregation is challenging, even with electron probe micro-analysis. In this study, a multiphase-field model coupled with the real thermodynamic data of Ti6Al4V alloy was successfully developed and applied to simulate the rapid solidification of columnar β grains via electron beam additive manufacturing. The thermal gradient (G) and cooling rate (R) were obtained from a 3D powder-scale multiphysics simulation and provided as inputs to a multiphase-field model. The effects of the electron beam process parameters and thermal conditions on the columnar β grains were investigated. Liquid films and droplets were observed to have solute enrichment in the intercellular region. The size of the liquid film increased at a lower scanning speed and energy power. Increasing the scanning speed and energy power refined the columnar β grains and decreased the liquid film size. The extent of microsegregation considerably increased at lower energy power, whereas the change in scanning speed had little effect on the microsegregation. The results also indicate that solute vanadium results in significant solute trapping and microsegregation during the rapid solidification of the Ti6Al4V alloy.     

Thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride irradiated with fast neutrons

A thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride U_0.8Pu_0.2(C_0.5N_0.5)_0.995 irradiated with fast neutrons was carried out with respect to temperature and burnout. In the temperature range of 900–2500 K, accumulation of fission products in fuel resulted in the formation of a multicomponent gas phase containing the following basic elements and compounds: volatile (Cs, Sr, Ba, Se, Te, I, Pd, CsI, Cs₂I₂, BaI, SrI, BaI₂, SrI₂, LaSe, TeSe, and LaTe), nitrogen-containing components (N₂, N, CN, CN₂, C₂N₂, UN, UN₂, PuN₂, CsN, CeN, LaN, YN, MoN, and ZrN), carbon-containing components (C, UC, UC₂, UC₄, PuC, PuC₂, PuC₄, ZrC, ZrC₂, YC₂, CeC₂, LaC₂, and NdC₂), and hardly volatile metals (U, Pu, Ru, Rh, Pd, Y, Ce, La, Nd, Tc, Mo, and Zr). The partial pressures of the said gas phase components over carbonitride fuel were calculated with respect to temperature and burnout (up to 18%).     

Thermodynamic aspects of inclusion engineering in steels

Tailoring non-metallic inclusions in accordance to the desired effect on steel properties has gained widespread acceptance in the last decades and has become known as “inclusion engineering”. Effective inclusion engineering involves three steps： （a） a good knowledge of how inclusions influence properties, （b） understanding what is the effect of each type of inclusions on these properties and thus which is the most desirable inclusion in a given product and （c） adjusting the processing parameters to obtain these inclusions. A significant portion of the process adjustment is done during steel refining, where the steel can be tailored so that the desired chemical composition of the non-metallic inclusions that will precipi- tate can be altered. Understanding the relations between steel chemistry, processing variables and inclusion chemical composition requires significant understanding of the thermodynamics of the systems involved. These complex equilibrium calculations are best done using computational thermodynamics. In this work some of the basic techniques used to control inclusion composition are reviewed and the thermodynamic information required to perform this task is presented. Several examples of the application of computational thermodynamics to inclusion engineering of different steels grades are presented and compared with experimental results, whenever possible. The potential and limitations of the method are highlighted, in special those related to thermodynamic data and databases.     

Compound formation and abrasion resistance of ion-implanted Ti6Al4V

Depth distributions and compounds of Ti6Al4V ion-implanted with carbon, nitrogen, platinum or gold were investigated using X-ray photoelectron spectroscopy. The microhardness and the surface damage occurring during wear tests against polyethylene were determined. The oxide film thickness is reduced by implantation of nitrogen or noble metals. Carbon or nitrogen implantation increases the microhardness, H, due to compound formation. The surface damage owing to removal of oxide particles from the titanium surface is reduced to various extents by different implantation conditions. Wear reduction is ascribed to an increase in microhardness and a decrease in oxide film thickness, D. A criterion to assess the influence of the film thickness on the wear behavior is derived. A characteristic parameter for abrasion resistance (R=H×D^−1/2) is suggested.     

含铌钼钢中微合金碳氮化物沉淀析出及其强化机制

利用物理化学相分析法、透射电镜、能谱分析和X射线衍射分析了两种热轧态的含铌钼低碳钢中微合金碳氮化物析出相的成分、形貌以及粒度分布等特征,结果表明,含铌钼低碳钢中钼可与铌一起析出,形成具有NaCl型面心立方结构的碳氮化铌钼析出相,且0．081Nb-0．14Mo钢和0．17Nb-0．12Mo钢的MC析出相中钼与铌的原子比分别为0．41和0．22。在这两种钢的MC析出相中小于10nm的碳氮化铌钼的质量分数分别为58．4％和66．1％,这些纳米颗粒呈弥散分布,其沉淀强化增量分别为179．3MPa和257．7MPa。并对钼铌复合析出的机制进行了讨论。     

Thermodynamic Interactions of Si and Ti in Liquid Cu

The activity coefficients of titanium in liquid Cu-Ti at 1623 and 1673 K were measured by equilibrating the liquids with Ti₃O₅ in a oxygen partial pressure controlled by C(s)/CO(g) equilibrium. Furthermore, the thermodynamic interaction parameter of silicon on titanium and the self-interaction parameter of titanium in liquid Cu-Ti-Si at 1773 K were determined by equilibrating the 58 mass% TiO₂-42 mass% CaF₂ slag with Cu-Si-Ti liquids. And the interaction parameters e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} and e_\textTi^\textSi e_{\text{Ti}}^{\text{Si}} obtained using a multiple regression were as large as −69.32 and 15.44 respectively. Based on the above determined value of e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} , the relationship between Henrian constant of titanium in liquid Cu-Ti melt, \upgamma_{\textTi(\texts)}⁰ \upgamma_{{{\text{Ti}}({\text{s}})}}^{0} , from 1473 to 1923 K was evaluated, and is expressed as:

Simulation of evolution of precipitates of two carbonitride phases in Nb- and Ti-containing steels during isothermal annealing

A model for describing the evolution of carbonitride precipitates of several compositions in steels at the stages of growth, dissolution, and coalescence is proposed. The kinetics of the growth and dissolution of carbonitrides in the Fe-Nb-Ti-C-N system is calculated based on the numerical implementation of this model.     

高速切削Ti6Al4V锯齿形切屑形成的表征

深入研究锯齿形切屑的形成过程及表征有利于工业生产中的切屑控制。用锯齿频率、锯齿化程度及绝热剪切带间距来对锯齿形切屑进行表征。鉴于Ti6Al4V在加工过程中易于形成锯齿形切屑,因此选择Ti6Al4V作为工件材料,通过高速切削Ti6Al4V实验,收集不同切削速度和每齿进给量下的锯齿形切屑;将获得的锯齿形切屑进行抛磨及腐蚀后,在VHX-600 ESO数码显微镜下观察切屑形貌,计算不同切削条件下锯齿频率、锯齿化程度及绝热剪切带间距。结果表明:随着切削速度的提高,锯齿频率及锯齿化程度增大,绝热剪切带间距减小;随着每齿进给量的增大,锯齿频率减小,锯齿化程度及绝热剪切带间距增大。锯齿化程度可以作为普通切削、高速切削及超高速切削的判据。