Cold Compaction Behavior Research Articles

Cold Compaction Behavior of Unsaturated Titanium Hydride Powders: Validation of Two Compaction Equations

Unsaturated titanium hydride (TiHX) powder has high formability and is a promising raw material for titanium-based powder metallurgy. In this work, TiH2, TiHX, and HDH Ti powders were characterized, the cold compaction behavior of the powders was investigated, and the densification mechanism was analyzed. The TiHX was a three-phase mixture containing an α plastic phase and δ and ε brittle phases through Rietveld refinement. The TiHX compacts had compressive strength of over 420 MPa (higher than TiH2 and similar to HDHTi) and relative density of over 80% (higher than TiH2 and HDH Ti) at 600 MPa. The Gerdemann–Jablonski and Cooper–Eaton equation were used to simulate the powder compaction curves and describe powder compaction behavior. The plastic deformation of TiHX powder is greater than TiH2, and the particle rearrangement is greater than HDH Ti during cold compaction. Such compaction behavior of TiHX causes an excellent green-strength–relative-density combination.

Experimental Testing and Fabrication of Metal Matrix Composite for Automotive Applications

Cold compaction behaviour, hardness, and micro-structural behavior of aluminium–boron carbide composites with variable boron carbide content for several composite systems, including Al-5 percent B₄C, Al-10 percent B₄C, Al-15 percent B₄C, and Al-20 percent B₄C, were all evaluated. Powder metallurgy was used to create the particle reinforced composite, with aluminum particles measuring 75 microns and boron carbide particles measuring 150 microns. The compacts were made using a universal testing machine (UTM) with a 60-ton capacity and the appropriate punch and die set assembly. After the green compacts were prepared, they were sintered in an electric furnace at 550°C for 120 minutes. The compacts are then allowed to cool in the furnace to room temperature. Cold compaction and axial pressing were used to study densification tendencies. The link between applied pressure and density, as well as between applied pressure and relative density, was established. The percentage of B₄C reinforcement was used to boost the hardness and compressive strength of various composite samples. Scanning electron microscopy (SEM) images were used to investigate microstructural phenomena. The final solution was compared to that of Cam, an existing car component. It's made of a metal matrix composite of Al-SiC. Because the Al-B₄C composite has a lower density than the Al-SiC composite, it allows for the most weight reduction in the product. The samples' weights have been reduced, resulting in a higher strength-to-weight ratio. In both cases, the material cost evaluations were substantially identical. It's simple to automate the fabrication process.

Comparative Study on Cold Compaction Behavior of TiH2 Powder and HDH‐Ti Powder

The compaction mechanism of titanium hydride powder is an important issue because it has a direct impact on density and strength of green compacts and ultimately on the physical and mechanical properties of a final sintered products. In this paper, the characteristics and compaction behavior of titanium hydride and hydrogenation‐dehydrogenation titanium powders are comparatively studied and analyzed for better understanding of compaction mechanism of brittle low‐strength titanium hydride. The results indicate that the particles of titanium hydride powder are easily crushed under compaction loading at relatively low pressure well below compression strength of bulk titanium hydride, the degree of particle crushed increases with the increase of pressure. The compaction behavior of titanium hydride powder mainly includes the rearrangement and crushing of particles in the early compaction stage, minor plastic deformation, if any, and further rearrangement of particle fragments with filling the pores in the later stage. Such compaction behavior provides relative density of green hydride compacts higher than that for titanium powder of the same size. The relatively coarse titanium hydride powder with wide particle size distribution is easier to fill the pores providing highest green density.

Cold compaction behavior and pressureless sinterability of ball milled WC and WC/Cu powders

In this research, cold compaction behavior and pressureless sinterability of WC, WC-10%wtCu and WC-30%wtCu powders were investigated. WC and WC/Cu powders were milled in a planetary ball mill for 20h. The milled powders were cold compacted at 100, 200, 300 and 400 MPa pressures. The compressibility behavior of the powders was evaluated using the Heckel, Panelli-Ambrosio and Ge models. The results showed that the Panelli-Ambrosio was the preferred equation for description the cold compaction behavior of the milled WC and WC-30%wtCu powders. Also, the most accurate model for describing the compressibility of WC-10%wtCu powders was the Heckel equation. The cold compacts were sintered at 1400?C. It was found that by increasing the cold compaction pressure of powder compacts before sintering, the sinterability of WC-30%wtCu powder compacts was enhanced. However, the cold compaction magnitude was not affected significantly on the sinterability of WC and WC-10%wtCu powders. The microstructural investigations of the sintered samples by Scanning Electron Microscopy (SEM) confirmed the presence of porosities at the interface of copper-tungsten carbide phases.

Consolidation of titanium hydride powders during the production of titanium PM parts: The effect of die wall lubricants

The effects of die wall lubricants on the cold compaction of titanium hydride powder are studied. Three commonly-used die wall powder metallurgy lubricants – zinc stearate, Acrawax® C dispersion and Mirror Glaze® – are compared. The influence of each lubricant on the cold compaction behaviour of titanium hydride powder was assessed with respect to the green density and strength, green compact ejection force, and the occurrence of green compact cracking. In addition, green compacts were sintered under vacuum at various sintering temperatures in order to determine the effect of the lubricants on oxygen content, phase compositions, microstructures and hardness of the sintered components. The results indicate that there is an immediate improvement in the cold compaction process when lubrication is used. The results further indicate that the lubricity of the lubricants is similar and most of the monitored variables are insensitive to the die wall lubricant used, the microstructures of the sintered components included. However, the use of Acrawax® dispersion resulted in more instances of green compact cracking, while zinc stearate tended to increase the oxygen content of sintered specimens due to the tentative decomposition of zinc oxide, a residual of the high temperature decomposition of zinc stearate.

Analysis of the Cold Compaction Behaviour of TiH<sub>2</sub>-316L Nanocomposite Powder Blend Using Compaction Models

The paper captures the effect of structure and the applicability of compaction models using the cold compaction of a TiH2-SS316L composite powder prepared by high energy mechanical milling. The composite blend was cold pressed uniaxially to pressures of up to 1250MPa. The compressibility of the composite blend was evaluated by fitting the experimental data to the most commonly used compaction models of Heckel, the Kawakita-Lüdde, the Cooper-Eaton, the Ge, and the Panelli-Filho compaction equations. Among the models, the Kawakita-Lüdde and Cooper-Eaton models fitted the experimental data very well with a good correlation (the correlation coefficient greater than 0.99) throughout the entire pressure range under investigation. The nature and mechanisms responsible for the densification during cold compaction are discussed. The Heckel, Ge, Panelli-Filho, and Cooper-Eaton model analysis showed that the dominant compaction mechanisms for composite blend were rearrangement of particles followed by elastic and plastic deformation. The results are discussed by way of a comprehensive model intercomparison study of the cold compaction behaviour using existing models.

Analysis of the Cold Compaction Behavior of Titanium Powders: A Comprehensive Inter-model Comparison Study of Compaction Equations

A brief background to compaction equations and their application to titanium powder is presented. The behavior and mechanisms of densification in selected titanium powders is critically analyzed by means of a comprehensive inter-model comparison of existing compaction equations. The results are discussed in terms of the comparative evaluation of cold uniaxial compaction tests of sponge Ti, CP TiH2, CP Grade 2 Ti, and TiH2-SS316L nanocomposite powder samples, which were conducted at applied compaction pressures of up to 1250 MPa.

Effects of Initial Powder Compact Thickness, Lubrication, and Particle Morphology on the Cold Compaction Behavior of Ti Powder

This work investigates the compaction behavior of hydride–dehydride CP-Ti powder from green density/compaction pressure curves. These were obtained through a modification of selected processing conditions, such as variation in compact thickness, the use of internal lubrication, and additions of plasma rotating electrode process powder. A modified Cooper–Eaton equation, which treats the compaction process to be a combination of particle rearrangement (PR) and plastic deformation (PD) mechanisms, was used to simulate the curves. A comparison with aluminum and iron compaction is also carried out in this study. The research indicated that the cold compaction of titanium powder can be separated into two stages: a PR stage (stage I), which occurs at a compacting pressure in the range of 0 to 200 MPa, followed by a further PR stage initiated by PD, when the compaction pressure is in the range of 200 to 1000 MPa. The existence of stage II is due to the low plastic deformability of titanium and low density achieved at the end of stage I.

Compressibility and solid-state sintering behavior of W-Cu composite powders

AbstractIn this research, compressibility and the effect of cold compaction pressure on sintered density of tungsten (W)-15% wt copper (Cu) and W-75% wt Cu composite powders were investigated. The powders were prepared by milling and reduction of WO3/CuO powder mixtures. The crystalline size and lattice strain of WO3 and CuO were determined using Debye-Scherrer’s formula after mechanical milling. Heckel and Panelli-Ambrosio equations were used to evaluate cold compaction behavior of the reduced powders. The results showed that Heckel equation represents better correlation between compaction pressure and relative density of W-75% wt Cu composite powders. However, it was confirmed that the preferred relation for evaluating the compaction behavior of W-15% wt Cu composite powders is Panelli-Ambrosio equation. The green compacts were sintered at 1000°C. It was shown that, by increasing the cold uniaxial pressure prior to sintering, the difference between green and sintered densities of W-15% wt Cu composite powder compacts was decreased. However, the W-75% wt Cu powders showed a different manner and higher compaction pressures led to higher densification during sintering.

Effect of Particle Size on Microstructure and Cold Compaction of Gas-Atomized Hypereutectic Al-Si Alloy Powder

The effect of particle size on the cold compaction behavior of rapidly solidified hypereutectic Al-27 wt pct Si alloy powder was studied by double action axial pressing at room temperature. The geometrical characteristics (morphology, size, shape, and distribution of Si reinforcing phase) and hardness of the powder as a function of the particle size were investigated. The result shows that finer powder particle size showed smaller primary Si particles and achieved a lower density at a given pressure. Whereas, the microhardness of Al matrix increases while the particle size decreases, which indicates that the supersaturation due to the high solidification rate increases the deformation resistance of the alloy powder. Furthermore, the geometrical characteristics of Si phases strongly depend on the particle size due to the suppressed growth of Si phases during atomization. This microstructural characteristic evidently affects the powder compactibility at high applied pressures.

Cold compaction behavior of nano-structured Nd–Fe–B alloy powders prepared by different processes

The compaction behavior of nano-structured Nd16Fe76B8 (atomic ratio) alloy powders, which were prepared by three different processing routes including melt spinning, mechanical milling in argon, and mechanically activated disproportionation by milling in hydrogen, was experimentally investigated by cold compaction tests. The compactibility was evaluated by using the double logarithm compaction equation, and both the hardening exponent, m, and the compaction modulus, M, were figured out for three powders by fitting the experimental data with the theoretical equation. The results show that the as-disproportionated alloy powders exhibits the best compactibility. By conventional cold compaction at 1400MPa, using the as-disproportionated alloy powders could reach an over 0.92 relative density, while the compact relative density for the other two powders was 0.8 under the same compaction conditions. Furthermore, the mechanisms responsible for the densification during compaction were discussed by referring to such factors as the powder morphology and phase constituent of the alloy powders.

Cold compaction study of Armstrong Process® Ti–6Al–4V powders

The Armstrong Process® developed by Cristal US, Inc./International Titanium Powder, is an innovative, low-cost technology for producing Ti and Ti alloy powders in a one-step, continuous process. In this work, Armstrong Ti–6Al–4V powders were characterized and the cold compaction behavior of the powders were investigated in detail. As-received as well as milled powders were uniaxially die-pressed at designated pressures up to 690 MPa to form disk samples with different aspect ratios. Samples with high aspect ratio exhibited non-uniform density along the pressing axis and the density distribution was consistent with the result predicted by finite element analysis. The model developed from the linear regression analysis on the experimental density data can be used to predict density of compacts with different aspect ratios. In the studied pressure range, an empirical powder compaction equation was applied to linearize the green density — pressure relationship. Cold compaction parameters were obtained for the as-received and milled Armstrong Ti–6Al–4V powders.

Comparison of sintering of titanium and titanium hydride powders

The cold compaction and vacuum sintering behaviour of a Ti powder and a Ti hydride powder were compared. Master sintering curve models were developed for both powders. Die ejection force, green strength and green porosity were lower for hydride powder than for Ti powder, all probably resulting from reduced cold welding and friction during compaction. For sintering temperatures above ∼1000°C, most of the difference in the sintered density of Ti and hydride is explained by assuming equal densification, while taking into account the lower green porosity of compacts made from hydride powder. However, there is evidence that particle fracture during compaction also contributes to increased sintered density for hydride powder. The Ti powder conformed to a master sintering curve model with apparent activation energy of 160 kJ mol−. The activation energy for Ti hydride also appeared to be about 160 kJ mol−, but the model did not fit the experimental data well.

Effect of nickel particle size on the compaction behavior of rotator mixed and mechanically alloyed nickel and aluminum powders

Elemental powder mixing prior to processes such as self-propagating high temperature synthesis (SHS) is a vital processing step that needs careful consideration. This is particularly true for powders with submicron particle sizes. The present paper investigates the effect of mechanical alloying of mixtures of aluminum and nickel (with different nickel particle sizes) on the dispersion and cold compaction behavior of the composite powders. The concepts of the theory of plasticity of porous bodies are also employed to assess the influence of mechanical alloying (MA) on the theoretical yield stress of the composite powder compact. It was found that after mechanical alloying, the yield stress increased only for nickel powder sizes equal to and greater than 5 μm.

Guidelines for modelling cold compaction behaviour of various powders

Through this study, the authors aim to anticipate powder behaviour by account of their intrinsic characteristics and thus giving guidelines for modelling industrial cold die compaction. Investigations are based on complete experimental testing of various industrial powders. Because of the very distinct material properties (metal or ceramic, presence of binder element or lubricant), as well as the morphology, these powders offer a wide range of compaction behaviours that are analysed in order to establish objective considerations for suitable modelling. A global overview of powder behaviour is then proposed, based on two behaviour subtypes regarding powder hardness. By analysing their main features (a new concept is also detailed) it is then possible to simplify the characterisation and modelling of any powder behaviour.

Yield behaviour of cold compacted composite powders

A triaxial test rig is used to study the axisymmetric cold compaction behaviour of powder composites comprising aluminium with silicon carbide reinforcement, and lead shot with steel reinforcement. Under hydrostatic loading the pressure–density response shows an increase in strength with increasing volume fraction of reinforcement. For a given volume fraction of inclusions, the compaction pressure to achieve a given relative density increases with diminishing size of reinforcement. The yield surfaces are measured after isostatic and closed-die compaction; it is found that the shape depends upon the deformation path, with greatest hardening along the loading direction. The effect of reinforcement on the overall shape of the yield surface is found to be minor.

Analysis of cold compaction densification behaviour of metal powders

Cold compaction behaviour of metal powders was analyzed using Shima, Fleck and Cam-Clay models. The Cam-Clay model reflects a very different plastic deformation mechanism for porous materials when compared with other two models. Brown's triaxial compressive experimental data (loading states: 1:1:1, 1:0.4:0.4, 1:0:0) were employed as the arbiter to these plastic models. It is very clear that only the Cam-Clay model can simulate well all experimental data under different loading states for iron and copper powders, while Shima or Fleck model can not. Therefore the Cam-Clay model is recommended to be used to analyze cold compaction densification process of metal powders.

Characteristics and sintering behaviour of zirconia ultrafine powders

Abstract Coprecipitation from water solution of chlorides was used to obtain yttria-stabilized zirconia powders. It was shown that precalcination processing of the coprecipitated gel greatly affects the microstructure of the resultant powder as well as its cold compaction behaviour and hence its sinterability. Relative densities of +98% theoretical have been achieved at sintering temperature as low as 1300°C.

Densification of silicon nitride powder with various additives

Cold compaction behavior of a sub-micron size silicon nitride powder with additives has been studied at various loading rates up to about 450 MPa. Liquid lubricants are found to be more effective than the solid lubricants. A marked increase in relative density has been obtained with the aid of 10 weight percent polyethyleneglycol after surface treatment of the powder with a dispersant solution. The loading rate between 0.8 and 800 MPa per minute has no effect on the densification process. Results are analysed with various theoretical equations available in the literature. The Cooper and Eaton's equation and also its modified form are used to determine the mechanism of densification during cold compaction.

Characteristics and sintering behaviour of zirconia ultrafine powders

Coprecipitation from water solution of chlorides was used to obtain yttria-stabilized zirconia powders. It was shown that precalcination processing of the coprecipitated gel greatly affects the microstructure of the resultant powder as well as its cold compaction behaviour and hence its sinterability. Relative densities of +98% theoretical have been achieved at sintering temperature as low as 1300°C.