Addition Of Process Control Agent Research Articles

OPTIMIZATION OF A METHOD FOR HIGH-ENERGY GRINDING OF POWDER MIXTURES OF THE Ti-Al-Nb SYSTEM IN THE PRESENCE OF STEARIC ACID AND TOLUENE

In this work, the influence of process control agents on the morphology and structural-phase state of powder mixtures of the Ti-Al-Nb system was studied. To improve the technique for grinding powder mixtures of the Ti-Al-Nb system in a planetary ball mill, two types of powders were prepared with the addition of process control agents based on stearic acid and liquid toluene. The process of grinding the compositions with the addition of agents was carried out at 550 rpm/m for 30, 60, 120, 180 minutes.During the studies, it was found that the evolution of particle morphologies using stearic acid and liquid toluene was similar. The effect of the agent as a process regulator of stearic acid on the evolution of powder morphology was greater than that of liquid toluene, since it inhibited the cold welding process of powders more effectively. During high-energy grinding using toluene for 120 and 180 minutes, undesirable carbide phases are formed.

Modification of cryomilling process to tailor geometrical characteristics of nanostructured Al powder for cold spraying

Cryomilling is the most commonly used method to fabricate ultra-fine grained (UFG) or nanostructured metallic powder. However, it has relatively low control over powder's geometric characteristics, particularly for the powders having FCC crystal structure. This shortcoming makes traditional cryomilling process unattractive to produce UFG/nanostructured feedstock for cold spraying process. In the present work, a modified pot vibration milling process was successfully employed to produce nanostructured powder of pure aluminum at 100 K. The geometrical characteristics of Al powder was controlled by using various combinations of the milling media (i.e. steel balls) of different sizes. The results indicate that with increase in milling time, the initial grain size of Al (~1–5 μm) was progressively refined to ~30–50 nm. Moreover, lamellar powder morphology was obtained with the addition of process control agent (PCA) while equiaxed polygonal structure was evolved without using PCA. It was also revealed that, in the absence of PCA, the particle size distribution was mainly controlled by the interstice size distribution of the milling media.

Compact Process for the Preparation of Microfine Spherical High-Niobium-Containing TiAl Alloy Powders

High-Nb-containing TiAl alloys are a new generation of materials for high-temperature structural applications because of their superior high-temperature mechanical properties. The alloy powders can be widely used for additive manufacturing, thermal spraying, and powder metallurgy. Because of the difficulty of making microfine spherical alloy powders in quantity by conventional techniques, a compact method was proposed, which consisted of two-step ball milling of elemental powders and subsequent radio frequency (RF) argon plasma spheroidization. In comparison with conventional mechanical alloying techniques, the two-step milling process can be used to prepare alloy powders with uniform scale in a short milling time with no addition of process control agent. This makes the process effective and less contaminating. After RF argon plasma spheroidization, the powders produced exhibit good sphericity, and the number-average diameter is about 8.2 μm with a symmetric unimodal particle size distribution. The powders perform high composition homogeneity and contain predominately supersaturated α 2-Ti3Al phase. The oxygen and carbon contents of the spheroidized powder are 0.47% and 0.050%, respectively.

One-Step Synthesis of BaCO<sub>3</sub> Nano-Particles via Mechano-Chemical Method

Barium carbonate (BaCO3) nano-particles were synthesized from the mixture of Ba(OH)2.8H2O and Na2CO3 by mechano-chemical route without any subsequent heat treatment of the as-milled powders. Effects of milling time and addition of process control agents (PCA) on the phase composition and morphology of products have been investigated. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that BaCO3 nano-particles were synthesized only after 10 minutes of mechanical milling and phase evolution was not taken place by further milling. SEM results indicated that pencil-like and globular-like were two major morphologies of the particles. Addition of stearic acid as a PCA resulted in homogenized globular-like nano-particles with a mean particle size of 54 nm.

Effect of Addition of Process Control Agent (PCA) on the Nanocrystalline Behavior of Elemental Silver during High Energy Milling

Mechanical Alloying (MA) or High Energy Milling has been a subject of great interest for last few decades. However, in the majority of the cases the investigations are confined to areas like alloying in binary or multi-component systems from premixed powders. Very little work has been reported on high-energy milling of pure metals. There are some reports on mechanical alloying of pure metals that undergo polymorphic transformation on milling, but relatively few papers have been reported in the literature pertaining to attrition milling of pure metals, which do not fall under this category. One such attempt has been made in this investigation by subjecting a noble metal like silver with fcc crystal structure to attrition milling. The present work deals with the investigation of the effect of addition of a process control agent (PCA) on the nanocrystalline behavior of elemental silver powder subjected to high energy milling in an attritor. Elemental silver powder was subjected to attrition milling with and without addition of stearic acid as PCA. The powder samples drawn at periodic intervals during the course of milling were subjected to characterization using techniques like XRD, SEM and DSC. The variation in particle shape morphology, crystallite size and lattice strain as a function of PCA was studied.

Nanocrystalline TiAl powders synthesized by high-energy ball milling: effects of milling parameters on yield and contamination

High-energy ball milling was employed to produce nanocrystalline Ti–Al powders. As sticking of the powders can be sufficiently severe to result in a near zero yield, emphasis was placed on varying milling conditions so as to increase the yield, while avoiding contamination of the powders. The effects of milling parameters such as milling tools, initial state of the powders and addition of process control agents (PCA’s) were investigated. Cyclohexane, stearic acid and titanium hydride were used as PCA’s. Milling was conducted either in a Cr–steel vial with C–steel balls, or in a tungsten carbide (WC) vial with WC balls, using either elemental or pre-alloyed powders. Powder samples were characterized using X-ray diffraction, scanning and transmission electron microscopy. In the absence of PCA’s mechanical alloying in a WC vial and attrition milling in a Cr–steel vial were shown to lead to satisfactory yields, about 65–80%, without inducing any significant contamination of the powders. The results suggest that sticking of the powders on to the milling tools is correlated with the phase evolution occurring in these powders during milling.

Influence of milling conditions on magnetic properties of Nd(Fe,Mo) 12N x compounds

Ball milling conditions were examined for the preparation of fine Nd(Fe,Mo) 12N x particles. The milling process with high ratio of ball to powder produced Nd(Fe,Mo) 12N x particles with low i H c and 4π I r. The decrease in 4π I r and i H c was attributed to population of α-Fe and particle aggregates that were formed during the milling. The addition of process control agents (PCA, e.g. stearic acid) prevented aggregation in the ball milling, however, a large amount of α-Fe was precipitated during the recrystallization and an improvement of magnetic properties, as hoped for, did not occur.

アルミニウム合金の機械的合金化におけるミリング助剤の作用

An aluminum alloy, 2024, has been mechanically alloyed with nickel to investigate the effects of three process control agents, i.e., zinc stearate, amorphous carbon and graphite, on milling process and powder characteristics. In milling aluminum powders, some process control agent must be used so that a balance between cold welding and fracturing is obtained. Zinc stearate has turned out to be a suitable additive for controlling milling processes. The influences of process control agents on mechanical property were assessed in tensile tests of extrudates of the mechanically alloyed powders. It was found that carbon and graphite gave good tensile strengths both at ambient temperature and at elevated temperatures. Although zinc stearate gave good room temperature tensile strengths, it was not so effective to improve elevated temperature strengths. It was found that the combined addition of process control agents offered a way to comply with various demands; for example, good control characteristics of milling process with excellent high-temperature strengths on the extrudates were achieved by a combined addition of zinc stearate and carbon.