A novel approach to predict green density by high-velocity compaction based on the materials informatics method

High-velocity compaction is an advanced compaction technique to obtain high-density compacts at a compaction velocity of ≤10 m/s. It was applied to various metallic powders and was verified to achieve a density greater than 7.5 g/cm^3 for the Fe-based powders. The ability to rapidly and accurately predict the green density of compacts is important, especially as an alternative to costly and time-consuming materials design by trial and error. In this paper, we propose a machine-learning approach based on materials informatics to predict the green density of compacts using relevant material descriptors, including chemical composition, powder properties, and compaction energy. We investigated four models using an experimental dataset for appropriate model selection and found the multilayer perceptron model worked well, providing distinguished prediction performance, with a high correlation coefficient and low error values. Applying this model, we predicted the green density of nine materials on the basis of specific processing parameters. The predicted green density agreed very well with the experimental results for each material, with an inaccuracy less than 2%. The prediction accuracy of the developed method was thus confirmed by comparison with experimental results.

Analysis of density and mechanical properties of high velocity compacted iron powder

A new method for producing higher density PM parts, high velocity compaction （HVC）, was presented in the paper. Using water atomized pure iron powder without lubricant admixed as the staring material, ring samples were compacted by the technique. Scanning electron microscopy （SEM） and a computer controlled universal testing machine were used to investigate the morphologies and the mechanical properties of samples, respectively. The relationships among the impact velocity, the green density, the sintered density, the bending strength and the tensile strength were discussed, The results show that with increasing impact velocity, the green density and the bending strength increase gradually, so the sintered density does. In addition, the tensile strength of sintered material is improved continuously with the sintered density enhancing. In the study, the sintered density of 7.545 g/cm^3 and the tensile strength of 190 MPa are achieved at the optimal impact velocity of 9.8 m/s.

Improvement of a High Velocity Compaction Technique for Iron Powder

Water atomized pure iron powder was compacted by high velocity compaction （HVC） with and without upper relaxation assist （URA） device. The influence of URA device on green density, spring back, green strength and hardness was studied. Morphological characteristics of the samples were observed by scanning electron microscope （SEM）. Green strength of the samples was measured by computer controlled universal testing machine. The results show that as stroke length increases, the green density, green strength and hardness of the compacts increase gradually. At the identical stroke length, the green density of the compacts pressed with URA devise was 2% higher than the compacts pressed without URA device. The green strength and hardness of the compacts pressed with URA device were higher than the compacts pressed without URA device. Furthermore, the radial spring back of the compacts decreased gradually with the increment in stroke length, whilst that of compacts prepared with URA device was lower.

High Velocity Compaction of Aluminum Powders

High velocity compaction process of atomized Al powders was studied. The green density, the maximal force and the withdraw force of specimen were investigated. The green density of atomized aluminum powder was obtained to be 2.68 g/cm3 and its relative density is about 99%. The maximal force increased proximately linearly with the compaction energy. The withdraw force was observed ranging between 30 and 70 kN. The radial spring back was less than 0.1%.

Simulation of high velocity compaction of powder in a two dimension mould using lattice Boltzmann method

This work presents a numerical study on the dynamic high velocity compaction of the metal powder. The analysis of the process is based on a mesoscopic approach using multi-speed lattice Boltzmann method. The boundary condition and the relaxation time are tailored to the situation. The dynamic compaction process is vividly presented and the shock wave can be easily found in the simulation. The density is analyzed in order to explore the mechanism of the high velocity compaction.

高速压制技术(HVC)在制备W-15Cu合金中的应用

在熔渗法制备W/Cu合金的过程中,采用细钨粉(1.85μm)制备的钨铜合金与采用粗粒度钨粉制备的钨铜合金相比组织更均匀,产品性能也更好。但以细钨粉为原料,采用传统压制工艺很难得到相对密度达到72.40%的W85骨架,因而得不到成分为W-15Cu的合金。本试验采用高速压制技术(HVC)成功获得相对密度达到72.40%的细粉W 85骨架,然后在氢气炉中,1400℃高温熔渗制备得到W85/Cu合金。采用扫描电镜(SEM)对钨铜复合材料的组织和成分进行观察与分析,并测定材料的密度、气密性、热导率和热膨胀系数。结果表明:采用高速压制技术结合熔渗工艺制备的W-15Cu材料相对密度达到99.5%;热导率为177W/(m·K),气密性(He吸附)为1.0×10-9Pa·m3·s-1和热膨胀系数(150℃)为6.9×10-6/K,各项性能指标均达到相应热沉材料的要求。

高填方路基强夯补强效果试验分析

文中以四川某高速公路改扩建项目为例,开展高填方路基强夯补强试验研究,并利用瑞利波法分析了补强前后高填方路基的密实度与瑞利波速的关系。结果表明,波速与压实度呈现近似线性增加的关系,波速每增加1 m/s,路基压实度增加0.19%。瑞利波监测法与现场灌砂法所有测量点位的压实度相差范围为3.5%左右,两种方法下的波速与压实度曲线相对一致。夯击后的夯击点密实深度显著提升,提升幅度在11.7%~18.7%,提升土体压实度可以有效提升路基土的施工质量。研究成果证明了瑞利波法测试土体压实度具有一定的可靠性,且采用的强夯方案有效提升了路基土的压实度,证实了高填方路基补强效果的可靠性。

高速公路高填方路基强夯补强施工及现场试验研究

文中结合某高速公路扩建工程实例,对高速公路高填方路基强夯补强施工技术及施工效果进行分析。结果表明,对路基进行强夯补强后可减少38.5%的沉降量,土体压实度提升了9%~23%,而有限元法和瑞利波检测法的计算结果与实测结果十分接近,说明了两种测试方法的可靠性。

UHMWPE模压成型方法与技术进展

目前,性能较好的超高分子量聚乙烯(UHMWPE)制品得到了广泛应用,但是,由于UHMWPE的黏度较高,难以输送、塑化和成型。模压成型是UHMWPE制品最主要的成型方式之一。首先,对最常用的普通静态模压(CM)成型方法进行陈述,分析并总结了成型温度、成型周期、成型压力以及冷却速率等模压成型参数对CM成型UHMWPE制品微观结构和性能的影响,发现,CM成型存在成型周期长、能耗高以及制品难以兼具良好的力学强度和耐磨性能等问题;其次,阐述了UHMWPE高速冲击(HVC)模压和超声模压的成型原理和特点,发现,引入动态力场后,能降低成型温度、缩短成型周期和减少能耗,但是,由于HVC成型UHMWPE制品韧性较差,超声模压成型制品力学强度较低。因此,动态模压成型方法是UHMWPE制品高效成型的重要研究方向之一。

Fourth order accurate compact scheme with group velocity control (GVC)

For solving complex flow field with multi-scale structure higher order accurate schemes are preferred. Among high order schemes the compact schemes have higher resolving efficiency. When the compact and upwind compact schemes are used to solve aerodynamic problems there are numerical oscillations near the shocks. The reason of oscillation production is because of non-uniform group velocity of wave packets in numerical solutions. For improvement of resolution of the shock a parameter function is introduced in compact scheme to control the group velocity. The newly developed method is simple. It has higher accuracy and less stencil of grid points.

粉末冶金温压工艺的研究进展及展望

温压是一项以较低的成本制造高性能粉末冶金零件的新型成形技术,本文综述并讨论了温压工艺的粉末原料、聚合物、温度、压力、烧结环节及致密化机理。在此基础上,介绍了温压工艺的新发展———流动温压、高压温压等,并对其应用前景进行了展望。

粉末冶金高速压制技术的原理、特点及其研究进展

本文简述了粉末冶金高速压制技术（High Velocity Compaction,简称HVC）的基本原理、主要特点及其研究进展.HVC技术是一项低成本、高效率成形高密度（7.4～7.8 g/cm3）粉末冶金零件的新技术.粉末在0.02 s之内通过高能量冲击进行压制,通过附加间隔为0.3 s的多重冲击波将密度进一步提高.HVC技术拓展了PM成形技术的应用领域,具有广阔的应用前景.

粉末冶金高速压制成形技术

瑞典Hydropulsor AB公司制造并出售其独创的液压冲击机后,解决了长期以来限制高速压制技术工业化应用的设备问题,该技术将得到极大的推动。本文介绍了高速压制技术的一些特点,如压制速度、压坯密度分布等。讨论了在生产过程中所应采用的压制速度、模具几何尺寸等技术问题。

提高粉末冶金制品压坯密度的新技术

粉末冶金是一项以较低的成本制造高性能铁基粉末冶金零件的生产技术。然而 ,其制备的粉末压坯密度通常较低 ,因而影响了零件的性能。在此介绍了几种提高粉末冶金零件压坯密度的新技术 ,如温压、流动温压、高压温压以及高速压制等 。

力与应力波对高速压制压坯质量的影响

高速压制时,在锤头冲击压制的过程中会产生一个力的扰动,这个扰动在模具及压坯里的传播即为应力波。应力波的存在是高速压制与常规模压的主要区别之一。本文分析了高速压制过程中应力波波形的基本特征,应力波呈锯齿波形,每一个加载波形上都有数个极值点。研究了应力波对压制结果的作用,应力波在自由端面反射后会造成拉应力,会导致压坯表面分层和剥落。

电解铜粉高速压制成形

研究电解铜粉高速压制成形工艺，探讨冲击能量、压制次数对生坯密度、最大冲击力和脱模力的影响。结果表明：当冲击能量为6076J时，试样的生坯密度达到最大，为8．42g／cm^3，相对密度约为95％；当冲击能量相同时，采用两次压制制备的试样的生坯密度较单次压制的高且前者的脱模力较低。高速压制过程中，最大冲击力随冲击能量的增加而逐渐增大，而脱模力较低，仅在45～90kN之间变化。

粉末高速压制成形密度分布的数值模拟及影响因素分析

将研究不连续体力学行为的离散单元法应用于粉末高速压制致密化过程的研究,将粉末视为黏弹性的离散颗粒,建立粉末高速压制过程颗粒接触模型及每个颗粒的基本运动方程,推导了力与位移表达的粉末高速压制黏弹性本构关系。基于PFC软件实现了铁粉高速压制过程中粉末颗粒二维流动情况及压坯密度分布的数值模拟,模拟结果的密度分布规律与实际压制的密度分布规律较为一致;利用数值模拟结果对影响压坯密度分布的摩擦因数、高径比、双向压制因素进行了具体分析。

粉末冶金高速压制成形的压制方程

瑞典Hydropulsor AB制造并出售其独创的液压冲击机后,解决了长期以来限制高速压制技术工业化应用的设备问题,使该技术得到极大的推动。文内介绍了高速压制的特点,如压制压力、压制速度、压坯密度分布,脱模压力等;对高速压制致密化机制进行了探讨,提出了“热软化剪切致密化机制”,据此给出了相应的压制方程lnφ=k1ΔHL/k2exp[k2(1-P/ΔHL)]+C。并利用实验数据进行了验证。结果表明,该方程具有满意的精度和广泛的适用性。

粉末冶金高速压制技术的研究进展

主要介绍了高速压制技术的特点和研究进展。高速压制技术是一项低成本、高效率成型高密度粉末冶金零件的新技术,由于具有良好的性价比而备受关注。其压制速度快,可使材料性能更加优良、生产更加经济化,具备用中小型设备生产超大零件的能力,具有广阔的应用潜力。

纯钛粉高速压制行为及其烧结性能研究

采用自主研发的机械蓄能式高速压机成形纯钛粉,研究纯钛粉高速压制成形行为及烧结坯的组织和性能。结果表明:经高速压制工艺成形的生坯密度随着冲击能量增加而增加。冲击能量为1805 J时获得的最高压坯密度为4.37 g/cm^3,相对密度达到96.9%。生坯的径向弹性后效随着冲击能量的增加而增加。在1200℃真空烧结后发现,随着冲击能量的增加和烧结时间的延长,烧结密度增加。烧结2.5 h后,获得的最高密度达到4.50 g/cm^3,相对密度为99.8%,最大硬度达到298 HV。当冲击能量为1805J烧结时间为1.5 h时,最高的抗拉强度达到638 MPa。径向烧结收缩率随着冲击能量增加而减少,而轴向烧结收缩率与冲击能量的关系不存在明显的规律。