Effect of transition metals on the grain size of titanium

Conclusions Additions of lanthanum, yttrium, nickel, palladium, and platinum are the most effective in refining the grains of cast titanium as compared with other transition metals investigated.Institute of Problems of Material Science of the Academy of Sciences Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 30–31, November, 1970.     

The determination of austenite grain size in ferrous metals

A simple uncomplicated method is introduced to render the austenite grain boundaries visible at room temperature. The suggested method is inexpensive and time saving and may be used universally. This is demonstrated on eleven ferrous materials and a good reproducibility is shown. The austenite grain sizes estimated by more complex methods are very similar to those determined by this new method.     

Self-similar grain size distribution in two dimensions: Analytical solution

Consideration of the physics and topology of two-dimensional grain growth suggests that a stochastic treatment is required to determine grain size distribution [Pande CS. Acta Metall 1987;35:2671]. In this paper, a size-based continuum stochastic formulation is presented based on topological considerations. As expected, this analysis leads to a Fokker–Planck equation for the size distribution, which should yield a unique self-similar asymptotic state that could be reached from any arbitrary initial state. The approximate solution of the Fokker–Planck equation presented here is limited to two dimensions and is based on the assumption of quasi-stationary distributions reached in the long time limit. The resulting grain size distribution is shown to be in agreement with that obtained from computer simulations, indicating the validity of the stochastic approach.     

晶粒尺寸对高强钢熔敷金属屈强比的影响

对不同层间温度下690 MPa级HSLA钢熔敷金属进行室温拉伸试验,探讨晶粒尺寸对熔敷金属屈强比的影响规律。应用电子背散射衍射技术统计熔敷金属的有效晶粒尺寸。结果表明:层间温度的降低使熔敷金属的屈强比升高,层间温度从200℃降低到80℃,屈强比由0.781增加到0.82。进一步研究表明:随着层温的降低,组织细化是屈强比升高的主要原因。     

基于BP神经网络的镁合金晶粒尺寸及流变应力模型

通过等温压缩试验研究了热变形条件对AZ61B镁合金再结晶晶粒尺寸及其流变应力的影响,并采用人工神经网络方法分别建立了动态再结晶晶粒尺寸及流变应力的模型。利用反向传播算法对网络进行试探性训练研究,得到了最佳参数。结果表明,所建立的网络模型具有优良的性能,能精确预测AZ61B合金热变形条件下的再结晶晶粒尺寸及流变应力。     

The effect of nickel hardness and grain size on acoustic and electromagnetic Barkhausen emission

Acoustic Barkhausen emission (ABE) and electromagnetic Barkhausen emission (EBE) have been measured during the magnetization of nickel. Of particular interest is the effect on the Barkhausen emission envelope as the microstructure of the material is varied. Samples of nickel were heat treated at temperatures up to 1100°C and the effect on ABE and EBE measured. Measurements on ‘as machined’, unannealed material indicate that EBE is unrelated to ABE since EBE evaluates surface condition, while ABE is generated within the bulk of material, and the machined surface and bulk conditions are different for an unannealed sample. On heat treatment the correlation between surface condition and bulk condition returns (as indicated by Barkhausen emission envelopes) and the correlation is considered to be due to the relative energies of break away of 71°, 180° and 109° domain walls. Measurements were made of hardness and grain size and the characteristics of the Barkhausen emission signals compared to hardness and grain size. Parameters used to characterize the Barkhausen emission signals include the time corresponding to the peak in the EBE signal (t_p) and the rms level of the ABE signal (V_rms). These parameters correlate well with material hardness and grain size and offer some potential for measuring these quantities.     

The effect of grain size and aging on hydrogen embrittlement of a maraging steel

Notched tensile tests were conducted under a slow displacement rate to evaluate the influences of grain size and aging on hydrogen embrittlement (HE) of T-200 maraging steel. In addition, an electrochemical permeation method was employed to measure the effective diffusivity (D_eff) and apparent solubility (C_app) for hydrogen of various heat-treated specimens. The results indicated that the aged (482 °C/4 h) specimens comprised of numerous precipitates led to a raised C_app and a decreased hydrogen diffusivity as compared to those of the solution-treated ones. The solution-treated specimens were resistant to gaseous HE, whereas aged specimens were susceptible to it, implying the strength level was the controlling factor to affect the HE susceptibility of the specimens. Nevertheless, all specimens suffered from sulfide stress corrosion cracking (SSCC) severely but to different degrees. The aged specimens were more likely to form intergranular (IG) fractures in H₂S but quasi-cleavage (QC) in H₂. For the solution-treated specimens, a fine-grained structure was susceptible to HE in H₂S and revealed mainly QC that differed from the IG fracture of the coarse-grained one. The fracture mode of the specimens could also be related to the transport path and / or the supply of hydrogen to the plastic zone of notched specimens in hydrogen-containing environments.     

Schlegel description of grain form evolution in grain growth

The paths of evolution of topological grain forms during grain growth are described in terms of number of faces, edges per face and face arrangements, as depicted by Schlegel diagrams and the topological events that change them. This “Schlegel tree” describes transitions to higher face classes by grain encounters at corners and to lower face classes by grain-pair separation at three-edged faces. Transitions within face classes are described through rearrangements that occur to neighboring grains during these events. The process is further described by probabilities of the different paths in terms of numbers of edges, corners and three-edged faces at which face gain and loss events occur. Schlegel data from separated grains and three-dimensional Monte Carlo and front-tracking simulations show good comparison. Grain form frequencies increase with increasing number of transition paths into them from other forms. The highest frequency forms have few or no three-edged faces, while those with the most three-edged faces are present the least. These observations suggest that three-edged faces are catalysts for topological change, and forms with higher frequencies of these have shorter residence times before transitioning to lower classes.     

Effect of the initial grain size on the final grain size of materials of bellows

Conclusions The final grain size of the material of measuring bellows is determined by the conditions of mechanical and heat treatment, and it depends little on the initial grain size; this makes it possible to eliminate acceptance control of the grain size of material for bellows in the state as supplied.Belorussian Polytechnic Institute, Pilot Plant of the Research Institute of Heat-Treatment Instruments (NIIteplopribor), Smolensk. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 50–51, January, 1985.     

Effect of grain size on high-temperature stress relaxation behavior of fine-grained TC4 titanium alloy

In order to analyze the effect of grain size on stress relaxation (SR) mechanism, the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650–750 °C. A modified cubic delay function was used to establish SR model for each grain size. A simplified algorithm was proposed for calculating the deformation activation energy based on classical Arrhenius equation. The grain size distribution and variation were observed by microstructural methods. The experimental results indicate that smaller grains are earlier to reach the relaxation limit at the same temperature due to lower initial stress and faster relaxation rate. The SR limit at 650 °C reduces with decreasing grain size. While the effect of grain size on SR limit is not evident at 700 and 750 °C since the relaxation is fully completed. With the increase of grain size, the deformation activation energy is improved and SR mechanism at 700 °C changes from grain rotation and grain boundary sliding to dislocation movement and dynamic recovery.     

The effect of ferrite grain size in 08? steel on corrosion current

Joint optical metallographic and electrochemical investigation of 08⩝ steel reveals a mathematical model for corrosion current as a function of the average grain size (along and across the rolling direction) and the relative size distribution of the ferrite grains.     

The effect of stress on grain boundary interdiffusion in a semi-infinite bicrystal

Chemical interdiffusion along a grain boundary in a semi-infinite bicrystal subjected to external stress normal to the boundary plane is considered. Plating out of diffusing atoms in the grain boundary partially relaxes the applied stress and modifies the driving force for diffusion. The resulting diffusion wedge formed at the grain boundary exhibits a time-independent shape, with all its linear dimensions growing with annealing time t, according to the t^1/3 law. The diffusion zone formed in the vicinity of the grain boundary is a combined result of the grain boundary diffusion and lattice drift, and is characterized by concentration discontinuities at its borders. The proposed model is applied to the analysis of liquid metal embrittlement in the Fe–In and Cu–Bi systems.