方解石对建筑卫生陶瓷高温塑性形变的影响

为减小样品的高温塑性形变量,在原有研究基础上,通过调整化学配比并引入方解石设计了新的配方。采用半干压成型工艺制备样品。烧成后对样品进行物理性能测试,并探讨最佳烧成温度和最佳配方。结果表明:综合性能最优的是经1280℃烧成的添加10%方解石的样品,其烧成收缩率是4.98%,吸水率为0.03%,气孔率为0.06%,体积密度为2.12 g/cm^3,高温塑性变形指数为3.98×10^(-6)/mm^(-1)。研究表明,高温塑性形变与样品的氧化物组成和烧成温度等因素有关,少量添加方解石的配方样品高温塑性形变量小,方解石的添加量应控制在一定范围内。

高透日用瓷坯体形变研究

传统日用瓷中通常引入一定数量的Na_(2)O,满足致密化和透光率的需求,其质量百分比一般不高于1.5%。进一步提高Na_(2)O含量有助于获得高透日用瓷,但极易导致坯体在高温烧结时产生大量低粘度玻璃相而变形。通过调整坯体中Na_(2)O含量、α-Al_(2)O_(3)的外加量及二者相结合的方法,控制高钠日用瓷坯体的高温塑性形变。结果显示,以伴生钠长石高岭土为主体,外加4 wt%α-Al_(2)O_(3)控制形变,在氧化气氛中经1310℃煅烧,得到透光率高达12.85%、白度为74,吸水率为0.09%的高透日用瓷,其坯体中Na_(2)O含量高达2.60 wt%,但塑形形变指数PDI只有3.15×10^(-6)mm^(-1),符合高档日用瓷的生产要求。

Modeling of deformation energy at elevated temperatures and its application in Mg-Li-Al-Y alloy

To control the superplastic flow and fracture and examine the variation in deformation energy,the stress and grain size of Mg-7.28Li-2.19Al-0.091Y alloy were obtained using tensile testing and microstructure quantification,and new high temperature deformation energy models were established.Results show that the grain interior deformation energy increases with increasing the strain rate and decreases with increasing the temperature.The variation in the grain boundary deformation energy is opposite to that in the grain interior deformation energy.At a given temperature,critical cavity nucleation energy decreases with increasing strain rate and cavity nucleation becomes easy,whereas at a given strain rate,critical cavity nucleation energy increases with increasing temperature and cavity nucleation becomes difficult.The newly established models of the critical cavity nucleation radius and energy provide a way for predicting the initiation of microcrack and improving the service life of the forming parts.

High temperature plastic deformation behavior of non-oriented electrical steel

High temperature plastic deformation behavior of non-orientated electrical steel was investigated by Gleeble 1500 thermo-mechanical simulator at strain rate of 0.01-10 s^-1 and high temperature of 500-1 200 ℃. The stress level factor （a）, stress exponent （n）, structural factor （A） and activation energy （Q） of high temperature plastic deformation process of non-orientated electrical steel in different temperature ranges were calculated by the Arrhenius model. The results show that, with dynamic elevation of deformation temperature, phase transformation from α-Fe to γ-Fe takes place simultaneously during plastic deformation, dynamic recovery and dynamic recrystallization process, leading to an irregular change of the steady flow stress. For high temperature plastic deformation between 500 and 800 ℃, the calculated values of a, n, A, and Q are 0.039 0 MPa 1, 7.93, 1.9× 10^18 s^-1, and 334.8 kJ/mol, respectively, and for high temperature plastic deformation between 1 050 and 1 200 ℃, the calculated values of a, n, A, and Q are 0.125 8 MPa1, 5.29, 1.0 × 10^28 s^-1, and 769.9 kJ/mol, respectively.

Excellent ductility and serration feature of metastable CoCrFeNi high-entropy alloy at extremely low temperatures

Seldom could metals and alloys maintain excellent properties in cryogenic condition, such as the ductility, owing to the restrained dislocation motion.However, a face-centered-cubic(FCC) CoCrFeNi highentropy alloy(HEA) with great ductility is investigated under the cryogenic environment. The tensile strength of this alloy can reach a maximum at 1,251±10 MPa, and the strain to failure can stay at as large as 62% at the liquid helium temperature. We ascribe the high strength and ductility to the low stacking fault energy at extremely low temperatures,which facilitates the activation of deformation twinning.Moreover, the FCC→HCP(hexagonal close-packed) transition and serration lead to the sudden decline of ductility below 77 K. The dynamical modeling and analysis of serrations at 4.2 and 20 K verify the unstable state due to the FCC→HCP transition. The deformation twinning together with phase transformation at liquid helium temperature produces an adequate strain-hardening rate that sustains the stable plastic flow at high stresses, resulting in the serration feature.

Modelling of grain boundary impurity segregation during high temperature plastic deformation

A modified theoretical model is proposed to predict the grain boundary segregation of impurity atoms during high temperature plastic deformation. The model is based on the supersaturated vacancy-impurity complex created by plastic deformation and involves quasi-thermodynamics and kinetics. Model predictions are made for phosphorus grain boundary segregation during plastic deformation in ferrite steel. The results reveal that phosphorus segregates at grain boundaries during plastic deformation. At a given temperature, under a certain strain rate the segregation increases with increasing deformation amount until reaching a steady value, and at the same deformation amount it increases with increasing strain rate. The predicted results are compared with the available experimental values, indicating that there is a reasonable agreement between the theoretical predictions and the experimental observations.