Influence Of Process Control Agents 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.

Fabrication of spark plasma sintered porous Ti-6Al-4V using PCA-added space holder method for bone implant materials

Ti-6Al-4V alloy has been used for bone implant materials. The porous Ti-6Al-4V lowers the mechanical misfit and prevents the implant loosening between bone and metal implant. The influence of sintering parameters, i.e., heating rate, sintering temperature, pressure, space holder size, and its distribution to the formation of both micro and macro- porosity is investigated. The initially developed image analysis of samples was used to quantitatively analyze the influence of process control agent (PCA) on the distribution of macro-pores. From the SEM results and samples relative density, it is found that the main parameter to control in the solid-state space holder method is space holder distribution, sintering pressure, and sintering temperature. Additionally, the most effective condition to produce less micro-porosity and more interconnectivity between macro-pore is the utilization of 10 wt% ethanol as PCA and sintering at 700 °C, 60 MPa.

Influence of process control agent and Al concentration on synthesis and phase stability of a mechanically alloyed AlxCoCrFeMnNi high-entropy alloy

This paper reports the effects of different process control agents (PCA) (methanol, n-heptane, and stearic acid) and aluminum concentration (x = 0.5, 1.0, and 1.5 at%) on the particle size distribution, structure, microstructure, stability, and prediction of phases in AlxCoCrFeMnNi high-entropy powder synthesized by mechanical alloying. The results showed that the vapor pressure, the polar nature of the different process control agents used, and type of milling (dry/wet) generating changes in the particle size distribution, microstructure, and crystalline structure since the use of PCA modifies the balance between the cold-welding and fracture processes. Quantitative analysis showed that the PCA chemical decomposition generated residual oxygen and carbon in all systems. X-ray diffraction showed that all systems present a mixture of crystal structures BCC-FCC with nanometric crystallite size, and the peak intensities changed in function of lattice deformation generated by type milling employed. On the other hand, the results also showed that the boundary between BCC-FCC and FCC regions is even broader and extends to higher Al concentration than those reported by the valence electron concentration criterion.

Influence of process control agents on microstructure and mechanical properties of Al alloy produced by mechanical alloying

The current study aims at comparing the effect of three different process control agents (PCAs)– namely methanol (ME), ethylene glycol (EG) and stearic acid (SA)– on microstructure and mechanical properties of Al–4.4Cu–0.5Mg alloy (AA) produced by mechanical alloying of elemental powders and subsequent hot extrusion. The effect of PCAs on particle size with milling time is insignificant. The average particle size of the milled powders of all samples has reached a steady state after 3 h. Even though the grain size and its distribution in all the samples in upset-forged, hot extruded, solutionised and peak aged conditions are similar, the number density and volume fraction of nanosized θ’ precipitates are observed to be higher in the case of AA–ME sample as compared to the other samples. AA–EG samples exhibited highest hardness when compared to the other samples. This can be attributed to the higher oxygen content in AA–EG sample that results in the formation of oxides that got dispersed in the matrix. Valid tensile test data was obtained only from AA–ME sample. The failure of AA–EG and AA–SA samples can be attributed to the presence of microcracks and higher oxide content. It can be concluded that nature of PCA has significant effect on oxygen pick up, size, number density and volume fraction of precipitates and in producing defect free bulk sample.

Role of Process Control Agent in the Synthesis of Multi‐Walled Carbon Nanotubes Reinforced Titanium Metal Matrix Powder Mixtures

The present study investigates the influence of process control agent (PCA), i.e., stearic acid (SA) on the dispersion of multi‐walled carbon nanotubes (MWCNT) into the titanium (Ti) matrix during mechanical alloying. A planetary ball mill was used in dispersing 0.5 wt.% MWCNT into the Ti matrix. The powder mixtures were prepared in two batches: without and with the addition of 0.5 wt.% SA. Green compacts of high energy ball milled powder mixtures were consolidated by using a uniaxial hydraulic press. Raman spectroscopy combined with X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were used to characterize the powder mixtures and green compacts. The evolution of MWCNT has been discussed in conjunction with the formation of nano crystalline TiC in the ball milled powder mixtures.

Influence of PCA on thermoelectric properties and hardness of nanostructured Ba–Cu–Si clathrates

Abstract Nanostructuring has been considered an effective approach to enhance the thermoelectric (TE) performance of materials by reducing their lattice thermal conductivity. In the present study, we show the influence of a process control agent (PCA) for ball milling, Stearic acid (SA), on the nano- and microstructure and thermoelectric properties of type-I clathrates in the Ba–Cu–Si system, which are promising candidates for TE applications. The SA effectively reduces cold welding and prevents particle agglomeration during ball milling. Consequently, it increases the powder yield and the milling efficiency. Smaller grain/crystallite sizes are obtained in the as-milled powders than without SA. Importantly, the SA forms nano-layers around the clathrate particles, which inhibit the grain growth during the hot pressing process used for powder compaction. Therefore, smaller grain sizes are also obtained in the hot-pressed samples. They show increased hardness and reduced thermal conductivity but also increased electrical resistivity. However, as the phonon transport is more strongly degraded than the charge transport, we observe 15% enhancement in the dimensionless thermoelectric figure of merit ZT by adding the PCA.

Influence of process control agent (PCA) and atmosphere during high‐energy ball milling for the production of particle‐reinforced aluminium matrix composites

AbstractEin geeignetes Verfahren zur Herstellung partikelverstärkter Aluminiumwerkstoffe ist das Hochenergie‐Kugelmahlen (HEM) mit anschließender Kompaktierung. Bei dem Mahlverfahren haben neben anderen Parametern gegebenenfalls eingesetzte Trennmittel (PCA – process control agent) sowie die Atmosphäre entscheidenden Einfluss auf die sich ausbildende Verbundpulverstruktur. Nach zahlreichen Forschungsbeiträgen auf dem Gebiet der partikelverstärkten Aluminium‐Werkstoffe der Autoren beschäftigt sich der vorliegende Beitrag mit der Evaluation verschiedener PCAs und mit dem Einfluss der unterschiedlichen Mahlatmosphären (Luft, Argon, Stickstoff) auf das Hochenergiekugelmahlen bei der Herstellung eines Verbundpulvers einer Aluminiumlegierung der 2xxxer Serie mit SiC‐Partikeln. Die Untersuchungen zeigen, dass die Reaktion des Mahlgutes mit Luft die Mahleigenschaften des Aluminiumpulvers deutlich verändern. Die Verwendung eines PCAs ist dadurch, anders als bei inerten Atmosphären, nicht mehr nötig. Für das Mahlen mit PCA wird Menthol als Alternative zur Stearinsäure aufgezeigt.

Influence of process control agents on the performance of Ni 3Al by mechanical alloying

The influence of process control agents (PCAs) on the mechanical properties of Ni 3Al intermetallic compounds by mechanical alloying was investigated in order to develop oxide deposition reinforced intermetallics. The PCAs in mechanical alloying were pure ligroin, 75 vol.% ligroin + 25 vol.% alcohol, 50 vol.% ligroin + 50 vol.% alcohol, 25 vol.% ligroin + 75 vol.% alcohol, and pure alcohol. The normal composition is Ni−22.9at.%Al−0.5at.%B, the ball-to-powder weight ratio is 10:1, and the milling time is 30 min. Then, the powders were sintered by spark plasma sintering under 40 MPa for 5 min at 1000°C. The results show that a higher bending strength and a higher hardness were obtained when the PCAs were 75% ligroin + 25% alcohol in mechanical alloying. The bending strength is about 2700 MPa and the hardness (HV) is more than 6 GPa.

Magnetic study and thermal analysis of a metastable Fe-Zr-based alloy: Influence of process control agents

In this work a Fe 60Co 10(Ni 70Zr 30) 15B 15 nanocrystalline alloy was produced by mechanical alloying. Powders were milled using hexane or cyclohexane as process control agents (PCAs) and their properties compared with those of alloy developed without PCA. Structural and magnetic analysis was performed using X-ray diffraction (XRD), transmission 57Fe Mössbauer spectrometry (TMS) and vibrating sample magnetometry (VSM). High magnetization of saturation and low coercitive field values correspond to an alloy milled with hexane. Thermal analysis was performed by differential scanning calorimetry (DSC). High thermal stability characterizes alloys milled with PCA. Annealing treatments at 400 °C improve magnetic behavior of all samples. Compositional analysis shows low-milling media (<1.1 at.%) and C contamination (<0.2 at.%).

Influence of process control agents in the development of a metastable Fe–Zr based alloy

In this work, a Fe–Zr based alloy prepared by mechanical alloying (MA) was investigated. The balance between cold welding and fracturing is controlled by the addition of a surface additive, a process control agent (PCA). Several PCAs such as hexane, polyethylene glycol, cyclopentane, naphthalene and hexanone were used. The results indicate that PCAs produce considerable effects on the particle size as well as on the structural behavior and thermal stability of the as milled powders, if compared with material synthesized without surfactant. We develop materials with higher thermal stability and disordered structure. Nevertheless, in other samples high crystallite size (>100nm) was found. Thermal analysis confirms the higher thermal stability of the disordered phase in the sample with hexane and naphthalene as PCA, probably due to C solid solution.

Influence of process control agent on interdiffusion between Al and Mg during mechanical alloying

The influence of a process control agent (PCA) on the reaction rate during mechanical alloying has been studied. Mechanical alloying of Al–Mg powder mixtures with different PCAs was carried out using a planetary ball mill. X-ray diffraction spectra showed that a small amount of PCA might lead to fast interdiffusion and reaction between Al and Mg although the crystalline sizes were in general the same for the powders when using different amounts of PCA. The fast interdiffusion and advanced reaction are closely associated with the diffusion distance between the powder particles due to the presence of PCA and to the actual weight ratio of ball to powder.

Prediction of the amount of PCA for mechanical milling

Abstract Process control agent (PCA) can strongly influence the size of ball milled powder particles. Experimental results show that the mean particle size is affected by: (1) the types of the PCA, (2) the amount of PCA, and (3) the milling duration. Two kinds of materials, namely Al and Mg, were used in the experiment and analysis of the influence of process control agent. It was found that there is a critical amount of process control agent below which the size of the powder particles tends to increase and above which it tends to decrease. In order to predict the amount of PCA required for a particular mean particle size under a particular milling duration resulting from a particular mechanical alloying process, a back-propagation neural network is employed. For each combination of base material and PCA, a neural network is trained using experimental data to achieve the correlation between the amount of PCA and a given particle size under a particular milling duration, i.e., PCA amount= f (particle size, milling duration). The testing results show that the trained networks have a fairly good generalization capability