Vanadium Alloy is a type of advanced nuclear material with many ideal properties compared as traditional nuclear materials, which has very wide and important application in first-wall and blanket structural material for fusion power plant applications. So it has attracted increasing attentions, especially on new manufacturing methods, such as selective laser melting and so on. In this paper, the comparative study of the powders obtained by mechanical mixing method, dry grinding method and wet grinding method respectively was performed to evaluate the effect of ball milling process on the microstructure and degree of alloying of the vanadium-based powder mixtures with the nominal composition of V 5Cr 5Ti vanadium alloy. The powders prepared by dry grinding method exhibits better spherical-like morphology and degree of alloying than those prepared by mechanical mixing method and wet grinding method, which indicates that dry grinding method can be used to prepare the superfine vanadium alloy powders for selective laser melting. This work provides a new method as well as important insights into the preparation of superfine vanadium alloy powders for selective laser melting additive manufacturing technology.
Vanadium Alloy has attracted increasing attention due to their wide range of applications in first-wall and blanket structural material for fusion power plant applications [
Fortunately, the development of additive manufacturing (AM) provides a powerful tool to obtain vanadium alloy parts. This process is characterized by large temperature gradient and rapid cooling rate, which thus result in a significant no equilibrium solute-trapping effect that avoids component segregation and relieves solubility limitations. At present, AM has been used for the manufacturing of many alloy parts by means of pre-alloyed powder including Ti-6Al-4V, high speed steel and so on [
Selective Laser Melting (SLM) has emerged as one mainstream technology of AM, which possesses the technical capacity of directly manufacturing precise metal parts in the industrial field [
Elemental powders with the average diameter of 35 μm including pure vanadium powder (purity ≥ 99.98%, granularity < 425 mesh), pure chromium powder (purity ≥ 99.98%, granularity < 425 mesh) and pure titanium powder (purity ≥ 99.9%, < 425 mesh) were accurately weighed to get the desired compositions V5Cr5Ti. The alloy was prepared through three different methods, which were mechanical mixing method, dry grinding method and wet grinding method respectively. Pre-weighed powder mixtures were canned into a QM-1SP4-CL high energy planetary ball mill machine by mechanical mixing method. Then, a high- energy ball milling process was performed at the rotation speed of 350 rpm for 1 h and this process used stainless-steel balls with a ball to powder weight ratio of 1.5:1, and the prepared powder sample was labelled as PM. Pre-alloyed Vanadium alloy powders were firstly prepared by dry grinding method. The high- energy ball milling process was performed at the rotation speed of 350 rpm for 5 hours, 10 hours, 15 hours, 20 hours and 25 hours, and the prepared powder samples were marked as D05, D10, D15, D20 and D25, respectively. This process used stainless-steel balls with a ball to powder weight ratio of 10:1. Secondly, another type of pre-alloyed vanadium alloy powders was prepared by wet grinding method. The high-energy ball milling process was performed at the rotation speed of 350 rpm for 5 hours, 10 hours, 15 hours and 20 hours, and the prepared powder samples were marked as W05, W10, W15 and W20, respectively. This process used stainless-steel balls with a ball to powder weight ratio of 10:1 and Acetone was added as a process control agent (PCA) to prevent excessive cold welding amongst the powder particles.
The property of the as-prepared powder samples was examined by X-ray diffractometry (XRD, D/max-RB, Ri-gaku, Japan) with Cu-Kα radiation. Scanning electron microscopy (SEM, LEO1530) with EDS analysis was used to examine the morphology of powders and the compositions of the samples. The particle size of all powder samples were examined by Laser diffraction particle size analyzer (Mastersizer 2000, Malvern instruments company, England).
The SEM images of vanadium-based powder mixtures with the nominal composition of V5Cr5Ti by mechanical mixing method and pre-alloyed vanadium alloy powders with the nominal composition of V5Cr5Ti by dry grinding method with different time were shown in
By comparing the SEM morphology of the mixed powders marked as PM with the pre-alloyed vanadium alloy powders including D05, D10, D15, D20 and D25, the change of the powder particle size and morphology of the powders can be easily observed. After dry grinding for 5h, the powders are consisted of large flat particles and small flat particles as displayed in Fig 1, i.e. D05 powder sample. It can be seen that the average particle size of powders after dry grinding for 10h is smaller than those of the D05 powders by dry grinding method and the particles change into spherical-like morphology. With the increase of dry grinding time (D15, D20, D25), the morphology of powders by dry grinding method get much more spherical. On the other hand, the change of particle size can be clearly observed, i.e. the particle size quickly gets small with the increasing of dry grinding time from 15 hours to 25 hours. According to the above results, the morphology evolution of the pre-alloyed vanadium alloy powder by dry grinding method is obvious with the increase of grinding time. Besides, when the dry grinding time is 5 hours, D05 powder sample has the particle size distribution with double peak.
For a further investigation into the particle size change of vanadium alloy powders by dry grinding method, laser diffraction particle size analyzer (LDPSA) has been used to study the particle size for different dry grinding time in terms of their average diameter. According to the LDPSA results (
tendency to increase first and then decrease. However, there is no obvious change of the particle size and morphology for mechanical mixed powders, i.e. PM sample, compared with initial elemental metal powders. So the LDPSA results are consistent with the morphology of powders by SEM.
The morphology and particle size distribution of pre-alloyed vanadium alloy powders with the nominal composition of V5Cr5Ti by wet grinding method with different time were shown in
decreasing with the increasing of dry grinding time. In addition, the peaks corresponding to Ti phase disappear when the dry grinding time reaches 5 h, which means that during the dry grinding process Ti phase and Cr phase have started to be solid soluted in V phase. Besides, when the dry grinding time exceeds 10 h, some new peaks appear. After calibration, these emerging peaks were identified to be corresponding to V (Cr, Ti) phase, which indicates the partial alloying of
V. According to the XRD results, it can be found that the pre-alloyed vanadium alloy powders by dry grinding method is constituted by V (Cr, Ti) phase, V phase and Cr phases.
degree of alloying than dry grinded powders due to reducing the elements diffusion rate by Acetone cooling effect.
The comparative investigation of the powders obtained by mechanical mixing method, dry grinding method and wet grinding method, respectively, was performed to evaluate the effect of ball milling process on the property of vanadium- based powder mixtures with the nominal composition of V5Cr5Ti vanadium alloy. It is shown that the pre-alloyed V5Cr5Ti powders by dry grinding method have a higher degree of alloying than wet grinded powders and mechanical mixed powders. Furthermore, dry grinding method can efficiently decrease the granularity of vanadium-based powder mixtures with the nominal composition of V5Cr5Ti vanadium alloy that is expected to be contributive to selective laser melting. After dry grinding 15 hours, the particles change into spherical-like morphology. With the increase of grinding time to 25 hours, the morphology of powders by dry grinding method gets much more spherical, and the granularity of particles decrease sharply. This work provides a new method as well as important insights into the preparation of superfine vanadium pre-alloyed powders for selective laser melting.
First of all, I would like to thank the financial subsidization (Project No.: 201103007) from science and technology of China Academy of Engineering Physics (CAEP). Specially thanks include the support from relative directors from Institute of Machinery Manufacturing Technology of CAEP and the critical guidance and help about milling process and property characterization of vanadium-based powders from professor Hongwu Ouyang of college of mechanical and electrical engineering, central south University of China, who has worked in state key laboratory for powder metallurgy, central south university of China. At last, I wish to show my great thanks to a lot of hard work on powders’ grinding experiments of lady Yali Fan in my research group.
Yang, J.L. and Li, J.F. (2018) Fabrication and Analysis of Vanadium-Based Metal Powders for Selective Laser Melting. Journal of Minerals and Materials Characterization and Engineering, 6, 50-59. https://doi.org/10.4236/jmmce.2018.61005