Francisco Ambrozio Filho

A study of a new phenomenological compacting equation

Abstract A new phenomenological compacting equation has been proposed. The equation is ln (1/(1−D))=A P +B where P is the applied pressure, D is the relative density of the compact, A is a parameter related to densification of the compact by plastic deformation, and B is a parameter related to powder density at the start of compaction. Linear regression analysis has been used to compare the new equation with the four compacting equations often used and proposed by Balshin, Heckel, Kawakita and Ge. The results show that the new equation gives linear correlation coefficients very close to unity. This equation, together with parameters A and B, permits improved evaluation of the compacting characteristics, compared to that performed by other equations.

An Investigation of the use of Stearic Acid as a Process Control Agent in High Energy Ball Milling of Nb-Al and Ni-Al Powder Mixtures

High energy ball milling of powders involves successive events of fracture and welding promoting mechanical alloying, fine and homogeneous dispersions could be attained. To minimize excessive cold welding during milling of ductile particles, the so called process control agents (PCAs) are added to the powder charges. These additives, mostly organic compounds, act as a coating of the particles inhibiting welding. It is known that PCAs are a source of contamination, so under this point of view its quantity much be the lowest possible. Moreover performing combustion synthesis of a powder mixture with PCA requires a pretreatment during the heating for extracting the PCA before reaction takes place, otherwise it can impair densification. In this work the use of stearic acid as PCA in milling Nb-Al and Ni-Al powder mixtures was investigated. The aim was to find a optimum quantity of that additive concerning milling action and decreased contamination.

Compaction of AISI M2+10%vol. NbC Processed by High Energy Mill

A mixture of AISI M2 + 10%vol. NbC was processed in an Atrittor high energy mill to obtain a composite powder. The milling time was varied during the process. The equation In(1/1-D)= A √P + B was used to fit the compacting experimental data from the composite milled powders. The linear correlation coefficients were better than 0.985 for all the composite powders. The parameters A and B from this equation were used to show how the composite powder characteristic changed after attritional milling.

Influence of the Heat Treatment on the Microstructure of AISI T15 High Speed Steel

The thermal history before the final heat treatment (hardening) of high speed tool steels affect the microstructure and, consequently the final properties of the tools. The influence of quenching temperature on the mean austenite grain size and size distribution and volume fraction of the primary carbides, MC and M 6 C, in AISI T15 samples prepared by hot isostatic pressing and liquid phase vacuum sintering was quantitatively investigated. The quenching temperatures were 1135, 1160, 1185, 1210 and 1235°C. The mean austenitic grain size as well as the distribution and the volume fraction of the MC and M 6 C primary carbides have been determined by analyses of the scanning electron micrographs using the Quantikov quantitative method. Specimens prepared either by hot isostatic pressing or by vacuum sintering show no modification in the mean grain size for increasing quenching temperature. Similar behavior was found for the measured carbide mean size. The mean size and the volume fraction of the MC and M 6 C carbides were similar for the hot isostatic pressed specimens. For the vacuum sintered specimens, on the other hand, the MC carbides present larger mean size and volume fraction, besides a larger fraction of coarse carbides (1,5-3 μm). The main results show that the quenching temperature increase of the AISI T15 steel does not influence both the mean grain and carbide sizes.

Effect of Wax Addition on Monel Synthesis by High Energy Milling

The effects of addition of polyethylene wax on the synthesis of Cu-Ni alloy (Monel) with 50wt%Ni processed in a high energy ball mill were investigated by X-ray diffraction. The Monel powder was characterized by laser particle size measurement and scanning electron microscopy. The results showed that the addition of wax at the beginning of milling causes a delay in alloy formation, and the particle shape obtained was essentially flaky. However, a strong effect was observed on the shape and particle size distribution when wax was added to the Monel powder with a flaky shape previously processed without wax. The particle shape changed from flake to more irregular and the median particle size decreased from 55 μm to 7.5 μm after 4 hours of milling.

The Influence of the Milling Media Environment on the Characteristics of a W-Cu Composite Powder

W-Cu composite powders were prepared by high energy milling under two milling environments: cyclohexane and air. Composite particles are formed in both cases. The W particles are fragmented and embedded into the Cu particles. Both, W and Cu, are heavily strained, mainly in the first hours of milling. The composite powder has high homogeneity and is much finer than the original Cu powder. The mean particle size of the powders milled in both conditions is very close, but the wet milling was near 25% longer than dry milling and the size distribution is wider. This is consequence of the higher milling intensity of dry milling.

High Energy Ball Mill Processing

The technique named mechanical alloying has been historically used for designating many different process routes, in spite of involving various kinds of materials and purposes. The aim of this work is to make a review of this technique, with special emphasis on the differences between those routes. Based on that, a suggestion for the classification of the various routes is presented. The high-energy ball mill processing can be divided in three main groups according to the mechanisms involved and/or the purpose envisaged: Mechanophysical conditioning, Mechanochemical synthesis and mix processes. In the first group, dissimilar or similar materials can be processed. In the second group, the materials can be synthesized with or without bonding changes during the process. The third one is a combination of the two first processes. Some examples are also presented.

Sintering of AISI M2 High Speed Steel with the Addition of NbC

The influence of adding 6 wt% (NbC) niobium carbide on the sintering temperature and microstructure of high speed steel - AISI M2 (0.87% C, 5.00% Mo, 6.00% W, 4,00% Cr, 2.00% V and Fe bal.) powder was studied. The starting material was obtained by vacuum melting followed by atomization in water. The samples were axially cold compacted in a cylindrical matrix and then vacuum sintered at 1250 and 1350 °C. Dilatometry and differential scanning calorimetry measurements indicated an increase in sintering temperature with addition of niobium to the AISI M2 steel. Optical and scanning electron microscope observations revealed a microstructure with uniformly distributed niobium carbides.

Preparation of Metal Matrix Aluminum Alloys Composites Reinforced by Silicon Nitride and Aluminum Nitride through Powder Metallurgy Techniques

The aliminium alloys are of particular interest to both the aerospace industry and automotive industry because of their attractive combinations of properties such as medium strength, formability, weldability, corrosion resistance and low cost. Compared with a metal matrix material, significant improvements in the mechanical and physical properties such as strength, toughness, and thermal conductivity can be achievied in metal matrix composites (MMCs). In this work of investigation aluminium alloy AA6061 was reinforced by 5, 10 and 15% (in mass %) of Si3N4 (silicon nitride) and AlN (aluminium nitride) by mechanical alloying in a vibratory type SPEX mill, cold uniaxial compaction and vacuum sitering in order to investigate the influence of the particulate phase in the microstructure and mechanical properties of the composites obtained. The microstructure of the powders and the sintered materials were evaluated by means of SEM and the hardness and were evaluated by hardness test.

Microstructural Characterization of Equiatomic NiTi Alloy Prepared by High Energy Milling

NiTi alloys with equiatomic composition of NiTi have the highest technological interest for its potencial application in differents areas such as biomedical, naval, aerospace, nuclear, automobilist , robotic,etc. In this work , it was used a 50Ni50Ti at % powder mixture, comercially pure, prepared by mechanical alloying in a Attritor with the following conditions: the milling speed and the ball charge were 1500 rpm and 10:1 respectively. The milling time was 2,4,8 and 16h, under an argon atmosphere at room temperature. After milling it was determined the particle size distribution, the phases by X-ray diffractions (XRD) and the powder morphology by scanning electron microscopy (SEM). The milling promotes dissolution of Titanium in Nickel and continuous amorphization by increasing the milling time. After 16h milling the alloy was almost amorphous. The powders after milling were compacted and heat treated at high temperature and microstructural evolution was characterized. In the heat treated samples were detected different phases showing heterogeneity in the alloy. The detected phases were Ni3Ti, NiTi, Ni2Ti and Ni2Ti4O. Contamination by milling was detected in the powder after milling and in the heat treated samples.