Showing papers in "Powder Metallurgy in 2002"
TL;DR: A short overview of works on spark plasma sintering (SPS) is given in the present paper as mentioned in this paper, however, the nature of activation effects, especially in its regards to acceleration of diffusion processes, is not clearly established.
Abstract: A short overview of works on spark plasma sintering (SPS) is given in the present paper. SPS is a newly developed rapid sintering technique with a great potential for achieving fast densification results with minimal grain growth in a short sintering time. It is proven by obtained experimental data that enhanced sinterability of powders subjected to SPS mainly associated with particle surface activation and increased diffusion rates on the contact zones caused by applied pulse current. Application of rapid heating results in bypassing of low temperature regions where surface transport controlled sintering is dominant. This preserves the powder surface area to temperature levels where bulk transport is significant. However, the nature of activation effects, especially in its regards to acceleration of diffusion processes, is not clearly established. A lot of research work reports about the occurrence of plasma during the application of pulse current. However, the appearance of thermal plasma during...
326 citations
TL;DR: In this article, three basic hypotheses regarding the effects of porosity and work hardening on powder compaction for building a new pressure-density relation are proposed, and complementary hypotheses are used for generalising the density description as a function of hydrostatic pressure and deviatory stress.
Abstract: In this paper, three basic hypotheses are proposed, regarding the effects of porosity and work hardening on powder compaction for building a new pressure-density relation. After a short validation on some hard powders, complementary hypotheses are used for generalising the density description as a function of hydrostatic pressure and deviatory stress. The model is then tested using triaxial characterisations from another author. Lastly, it is shown that the modelling parameters, to which a physical meaning is given, can be determined from two simple experiments, such as isostatic compaction and die pressing. This represents a drastic saving in time for characterising the compaction behaviour of hard powder.
40 citations
TL;DR: In this article, a single-action uniaxial pressing of a mixture of al-TiH2 powder mixtures was performed at 800°C for 5 min, and foaming was only observed for precursors with a theoretical density above 94%.
Abstract: Al-TiH2 powder mixtures have been cold compacted into precursors for foaming using single action, uniaxial pressing. After heat treatment, at 800°C for 5 min, foaming was only observed for precursors with a theoretical density above 94%. This density limit corresponds to the transition from interconnected to closed porosity, confirming that isolating porosity and enveloping the foaming agent in the matrix are vital to successful foaming. Although the variation in foam density for similar samples was small, the cell structures were different indicating that a low variation in foam density is not necessarily a good indication of achieving reproducible foam structures. The orientation of the sample had little effect on the foaming response for compacts with a length to diameter ratio below 1:2. For longer samples the foaming response was not uniform along the length of the sample indicating that in complex pressings the variation in local pressure must be understood in order to avoid regions being c...
33 citations
TL;DR: In this paper, the compaction and yield response of two steel and two copper powders were examined in a computer controlled triaxial cell, where concentration is on the response during simulated, frictionless closed die compaction, whereby the radial stress is controlled so as to keep the radius of the sample constant.
Abstract: In this paper the compaction and yield response of two steel and two copper powders are examined. These were chosen to determine how the material response depends on the type of material and the morphology of the powder particles. Experiments were conducted in a computer controlled triaxial cell. Here, concentration is on the response during simulated, frictionless closed die compaction, whereby the radial stress is controlled so as to keep the radius of the sample constant. The compaction process was stopped at regular intervals and a series of probing paths were followed in stress space to construct the yield surface for the compact.The experimentally determined yield surfaces are compared with yield surfaces predicted by empirical models and micromechanical models of the Fleck type, which assume that the compact consists of monosized spherical particles. During the early stages of compaction the form of the yield surfaces for spherical powders are consistent with Fleck's micromechanical model, ...
32 citations
TL;DR: A commercially available PM Al-5.5Zn-2.6Cu (wt-%) alloy has been used to study the effect of elemental Mg additions, ranging from 0 to 4.5 wt-%, on its sinterability and mechanical properties after sintering and heat treatment of the W and T6 type as mentioned in this paper.
Abstract: A commercially available PM Al-5.5Zn-2.5Mg-1.6Cu (wt-%) alloy has been used to study the effect of elemental Mg additions, ranging from 0 to 4.5 wt-%, on its sinterability and mechanical properties after sintering and heat treatment of the W and T6 type. DSC experiments were performed to study the chemical reactions occurring during sintering. Results obtained from dilatometry and DSC experiments were used to aid determination of the optimum sintering cycles under nitrogen. DSC experiments performed on as sintered samples were used for the determination of the solution treatment temperature. The microstructure obtained after sintering of the experimental Al alloys was characterised by SEM and XRD. The mechanical properties of the alloys, both, in the as sintered and heat treated states were obtained from tensile testing and hardness measurements. Additional theoretical calculations, using the THERMOCALC programme, along with the experimental observations, were carried out as an alloy design method...
32 citations
TL;DR: In this article, a method to simulate die compaction and sintering is presented by implementing user defined routines for both processes into the general purpose finite element program ABAQUS quantitative predictions of density distributions and shape distortions can be obtained as well as the stresses in the tool components.
Abstract: A method to simulate die compaction and sintering is presented. By implementing user defined routines for both processes into the general purpose finite element program ABAQUS quantitative predictions of density distributions and shape distortions can be obtained as well as the stresses in the tool components. By computational optimisation of the individual production steps suggestions can be made to improve the final properties. As an example for both die pressing and sintering a complex three-dimensional part is simulated and suggestions to improve dimensional accuracy are made. Finally, stresses in the tools are calculated showing that the deflections are large enough to cause punch to punch contact so that tool wear must be expected.
30 citations
TL;DR: Thematic Network PM Modnet was used to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results as mentioned in this paper.
Abstract: The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.
28 citations
TL;DR: In this article, density variations are addressed, both why they occur and what problems arise due to filling induced density variations, in powder metallurgy, and the results of these problems are discussed.
Abstract: Filling induced density variations is a problem that has long been overlooked by powder metallurgy scientists. In this paper,densityvariations are addressed, both why they occur and what problems t ...
22 citations
TL;DR: A review of recent progress in modelling and numerical simulation of powder compaction can be found in this paper, drawing on work presented in the Dienet Workshop and modelling sessions of Euro PM2001.
Abstract: Recent progress in modelling and numerical simulation of powder compaction is reviewed, drawing on work presented in the Dienet Workshop and modelling sessions of Euro PM2001.
20 citations
TL;DR: In this paper, the interplay between porosity and matrix strength in determining their tensile and impact behavior was investigated. But the authors focused on the fracture mechanism and not the porosity.
Abstract: Sintered steels in the density range 6.7-7 g cm- 3 and with a wide range of matrix hardnesses were produced with the main objective of understanding the interplay between porosity and matrix strength in determining their tensile and impact behaviour. The materials can be subdivided into two groups, characterised by different deformation and fracture mechanisms. The first group pertains to the as sintered materials (with a microhardness lower than 350HV0.1).They are characterised by a strain hardening stage before fracture, and both tensile strength and impact fracture load increase as density and matrix strength are increased. The second group pertain to the heat treated materials with a higher matrix hardness. These materials are characterised by a macroscopically brittle behaviour, since fracture takes place before general yielding. Because of the high matrix hardness, the peak stresses at the pore edges are not relieved by plastic deformation, and the pores behave as internal cracks. Fracture i...
19 citations
TL;DR: In this paper, the authors explored the use of a shear plate technique to measure the frictional characteristics between a compacted powder and a target surface and confirmed that the technique is valid to measure these frictional properties and that any variability in the data is a physical characteristic of the powder being tested.
Abstract: The paper explores the use of a shear plate technique to measure the frictional characteristics between a compacted powder and a target surface. The study confirms that the shear plate technique is valid to measure these frictional characteristics and that any variability in the data is a physical characteristic of the powder being tested. Surface roughness and hardness were explored fully for both iron and an alumina powder. This confirmed the major impacts of surface hardness, roughness, and roughness orientation on the friction coefficient. The static and dynamic values were found to be a minimum for the hardest surface (tungsten carbide). With regard to static friction, benefit may be obtained by using a very smooth surface finish, however, the minimum level of dynamic friction coefficient is not always associated with the smoothest surface.
TL;DR: In this article, a new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropics, die compaction, and creep tests.
Abstract: Most of the numerical simulation software on the hot isostatic pressing (hipping) process is based on viscoplastic modelling of densification, such as the well known Abouaf's model. These constitutive equations are generally obtained from a viscoplastic potential depending on Green's equivalent stress. An implicit coupling between isotropic and deviator parts is therefore only defined by an equivalent stress. A new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropic, die compaction, and creep tests. This paper deals with the presentation of this new formulation which has been implemented in the finite elements software PreCAD, and the subsequent changes observed in numerical simulations. These simulations achieved with PreCAD software, are compared with an experiment on a complex part manufactured by CEA Grenoble.
TL;DR: In this paper, the authors investigated the possible causes for shape changes of Distaloy AE powder compacts during sintering and proposed a simple analytical model to estimate the average effective viscosity of the material from the measured deformation.
Abstract: The possible causes for shape changes of Distaloy AE powder compacts during sintering are investigated. Conventional test bars have been sintered either on a flat base or on two far apart supports. The first tests showed the influence of green density on the shrinkage. A significant anisotropy is observed for the highest green densities, i.e. the axial shrinkage in the pressing direction is higher than the shrinkage in transverse directions. In the second tests, the test bars bent owing to gravity induced stresses. Through a simple analytical model, the average effective viscosity of the material has been estimated from the measured deformation. This value is compared with the viscosities directly measured during dilatometric tests with axial loading. The interest of these results for predicting shape changes during sintering of industrial parts is finally discussed.
TL;DR: In this paper, the microstructure of SLS samples heated to 1120°C for 3 h in 30H2-70N2 atmosphere at 2 K min-1 consisted of a mixture of austenite, M23C6, and Cr2N phases.
Abstract: At present, the research on rapid tooling by the selective laser sintering (SLS) method is mainly focused on the production of parts with high accuracy and definition. Very little effort has been devoted to the microstructural evolution and mechanical properties of this material. This paper gives detailed information about microstructural development and mechanical behaviour of Rapidsteel material after subsequent heat treatment cycles for binder removal, partial sintering, and liquid phase infiltration.The microstructure of SLS samples heated to 1120°C for 3 h in 30H2-70N2 atmosphere at 2 K min-1 consisted of a mixture of austenite, M23C6, and Cr2N phases. Subsequent infiltration of the above sample with bronze at 1050°C for 2 h in 30H2-70N2 atmosphere at 2 K min-1 produced similar phases together with an additional α(Cu-Sn) phase. The mechanical tensile fracture strength of the partially sintered part increased ten times after infiltration with bronze. However, the fracture behaviour is found to...
TL;DR: In this paper, the authors present guidelines for the turning and drilling of parts made with sinter hardenable powders, as well as a discussion on the effect of manganese sulphide particles and chip formation during turning.
Abstract: The constant demand for improved mechanical properties and lower production costs of PM parts has lead to the development of sinter hardenable steel powders. These powders produce fully martensitic microstructures by appropriately controlling the cooling rate during the sintering operation. Thus, the heat treatment operation (oil quenching) that would generally be required to obtain hardened parts can be eliminated. However, machining of the relatively hard sinter hardened parts is difficult.It then becomes critical to optimise the tool selection and the machining conditions, such as surface speed and feed. This paper presents guidelines for the turning and drilling of parts made with sinter hardenable powders, as well as a discussion on the effect of manganese sulphide particles and chip formation during turning.
TL;DR: In this paper, the same composition was employed to make powder injection moulded compacts with the expectation that even better mechanical properties would be attained, and the results obtained on the compacts sintered at 1200°C for 1h showed a tensile strength, hardness, and elongation of 685MPa, 91 HRB, and 7 5% respectively.
Abstract: Powder injection moulding (PIM) is a relatively new process and only a few alloy standards have been recognised. To further promote the application of this technology, new alloys with competitive mechanical properties need to be developed. Fe-1.75Ni-0.5Mo1.5Cu-xC is one of the compositions widely used in the conventional powder metallurgy industry in making press and sinter parts. To benefit from the excellent mechanical properties and the accumulated knowledge of this alloy system, the same composition was employed in this study to make powder injection moulded compacts with the expectation that evenbetter mechanical properties would be attained. The results obtained on the compacts sintered at 1200°C for 1h showed a tensile strength, hardness, and elongation of 685MPa, 91 HRB, and 7 5% respectively. With heat treatment, the tensile strength and hardness increased to 1530MPa and 52 HRC, respectively. However, the elongation decreased to less than 1 0%. These properties are better than those of th...
TL;DR: In this article, the authors proposed a method to improve further control over particle characteristics and to extend the process to production of other metallic powders, such as aluminium and ceramic powders.
Abstract: Tetronics plasma reactors are capable of producing nanosized aluminium and ceramic powder at rates of kilograms per hour with impressive process control. Work is under way to improve further control over particle characteristics and to extend the process to production of other metallic powders.
TL;DR: In this article, a new approach to produce ultrafine WC/Co powder by a mechanochemical process was made to improve the mechanical properties of advanced hardmetals and to cut production costs.
Abstract: A new approach to produce ultrafine WC/Co powder by a mechanochemical process was made to improve the mechanical properties of advanced hardmetals and to cut production costs. For powder preparation, the water soluble salts containing W and Co components were used as starting materials. After synthesis of the precursor powder from an aqueous solution by a spray drying technique, a salt removing heat treatment in air atmosphere was carried out to prepare the oxide powder. The oxide powder was mixed with carbon black by ball milling and this mixture was converted at 800oC to the nanophase WC/Co powder in H2 and N2 atmospheres. The average size of the WC particle was 100-150 nm. The possibility of achieving high density sintered material with an ultrafine and homogeneous microstructure using grain growth inhibitors, such as tantalum and vanadium carbides, has been shown.
TL;DR: A method for the production of Cu-Al2O3 composite powder has been suggested in this article, where aggregated Cu based powders with a homogeneous distribution of γ-Al 2O3 particles of about 25 nm in diameter have been synthesized The content of alumina in the powders was varied in the range of 2-1 6wt-%
Abstract: A method for the production of Cu-Al2O3 composite powder has been suggested in the present study Agglomerated Cu based powders with a homogeneous distribution of γ-Al2O3 particles of about 25 nm in diameter have been synthesised The content of alumina in the powders was varied in the range of 02-1 6wt-% The synthesised powders were hot extruded to full density with an extrusion ratio of 92% Mechanical properties and electric conductivity of as extruded bodies were measured to investigate the possibility of its application as an electrode As compared with selected commercial samples, superior electric conductivity and the same mechanical properties have been achieved
TL;DR: In this paper, the bending green strength of compacts was measured by uniaxial pressing of metal powders at 290 MPa and showed both surface roughness and micrometer sized primary grains.
Abstract: Metaliron powders of well controlled size and morphology were synthesised by thermal decomposition under hydrogen of precipitated ferrous oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strengths of compacts were measured.The precipitation of β-FeC2O4.2H2O oxalate from ammonium oxalate gives rise to the formation of spherical particles by aggregation ofelongated grains. Thermal decomposition of this oxalate from 400 to 500°C under hydrogen permits metal iron particles with a rough surface to be obtained. Decomposition occurring above 500°C induces a smoothness of the particle surface. Metal particles synthesised at 500°C show both surface roughness and micrometer sized primary grains.This specific microstructure has allowed the highest value ofcompact green strength (31·7 MPa) to be obtained.Acicular shaping of the β-FeC2O4.2H2O particles precipitated from oxalic acid involves, after decomposition, an increase in the surface roughness and ...
TL;DR: In this article, the properties of prealloyed Fe-1·5Mo base powder with and without additions of elemental Si, ferrosilicon, and carbon under various process conditions have been investigated.
Abstract: Alpha phase sintering, sinter hardening, and mechanical properties of prealloyed Fe-1·5Mo base powder with and without additions of elemental Si, ferrosilicon, and carbon under various process conditions have been investigated. Liquid paraffin, as a new lubricating agent, was found to be useful in reducing segregation, interparticle and die wall frictions, as well as reducing ejection forces and die and tool wear. It was found that addition of Si to the base powder enhanced the sintering process by stabilisation of the α-phase and formation of two kinds of liquid phase at ~1045 and ~1180°C, corresponding to the solidus and liquidus temperatures, respectively. This addition increased the tensile strength of the as sintered Fe-1·5Mo from 174 to 445MPa owing to massive solid solution strengthening effect of Si. An optimum sinter hardenable alloy, of composition Fe-1·5Mo + 3Si + 1·2C, provided a high sintered density of 7·55g cm-3, tensile and bend strengths of7 64 and 1405MPa, respectively, with 2·5%...
TL;DR: In this article, the authors investigated the use of a simple drop weight instrumented impact loading facility to produce metal powder compacts with better qualities than attained by the conventional means, and the results showed that the dynamic compaction specimens attained better densification and dimensional accuracy than quasistatic specimens.
Abstract: This paper investigates the use of a simple drop weight instrumented impact loading facility to produce metal powder compacts with better qualities than attained by the conventional means. Experiments were performed on Fe powder, Fe-C-Cu-Mn powder mix, and Cu-Zn powder mix at different height to diameter ratios and compacted at different energies. The overall density, density variation within the compact, dimensional accuracy, and microstructure were compared with quasistatic specimens compacted using conventional hydraulic press. The results showed that the dynamic compaction specimens attained better densification and dimensional accuracy than quasistatic compaction specimens.
TL;DR: In this paper, the analysis of research results concerning the application of PM technology to produce porous implantation material from Co-Cr-Mo alloy was presented, where Rotary cold re-pressing and heat treatment has been used to increase the density and mechanical properties of sintered samples.
Abstract: This paper presents the analysis of research results concerning the application of PM technology to produce porous implantation material from Co-Cr-Mo alloy. Rotary cold re-pressing and heat treatment has been used to increase the density and mechanical properties of sintered samples. The microstructure, hardness and compressive properties, and ultrasonic data of the obtained materials were investigated. The material had about 10% of porosity and has higher mechanical properties, i.e. UCS and plastic strain, compared with cast cobalt alloy, and had 25% lower values of Young's modulus and shear modulus.
TL;DR: In this paper, commercial tungsten carbide (WC) was coated with cobalt (Co) using a chemical precipitation technique and the coated powders were characterised for chemical composition and uniformity of coating.
Abstract: Commercial tungsten carbide (WC) was coated with cobalt (Co) using a chemical precipitation technique. The coated powders were characterised for chemical composition and uniformity of coating. TEM and SEM were used to observe the nature of the cobalt coating on WC particles. The coated powders were consolidated to near theoretical densities under varying temperature and pressure conditions using the plasma pressure compaction (P2C) technique in about 3 min. The consolidated samples were characterised by measuring transverse rupture strength, hardness, and microstructure. A maximum Vickers hardness of 2400 and transverse rupture strength of 2500 MPa was obtained for a sample consolidated at 1600°C and 40 MPa.
TL;DR: In this paper, a 2014 alloy manufactured through mechanical alloying was used as the matrix, and three different Fe3Al intermetallics have been used as reinforcement, also manufactured through a T6 heat treatment.
Abstract: Mechanical properties and wear behaviour of an aluminium matrix composite reinforced with Fe3Al intermetallics have been studied. A 2014 alloy manufactured through mechanical alloying was used as the matrix. Three different Fe3Al intermetallics have been used as reinforcement, also manufactured through mechanical alloying. The difference between them was the different mechanical alloying times (5 and 20 h were used) and the possibility of carrying out a heat treatment at 1000°C (on the 20 h milled intermetallic) before admixing to the aluminium matrix. The processing of these composite materials included mixing and cold compacting (conventional powder metallurgy) followed by hot extrusion (without caning and degassing). The effect of a T6 heat treatment was also evaluated. The influence of intermetallic additions on the mechanical properties (hardness and tensile strength) and wear behaviour (pin on disk test) was established. All intermetallics showed a good link with the matrix, and high reacti...
TL;DR: In this paper, a mixture of elemental powders with martensitic 410L steel has been used as a sintering aid to reduce compressibility and promote densification of the steels.
Abstract: Duplex stainless steels prepared from mixes of elemental powders with martensitic 410L steel have been shown to possess stable dual phase microstructures. Following heat treatment, the steels possess good mechanical properties. The addition of boron as a sintering aid reduces compressibility but promotes densification through transient liquid phase sintering; its effect on corrosion resistance is particularly favourable.
TL;DR: In this paper, the oxygen content in the process of the production of oxide dispersion strengthened copper by mechanical alloying was traced by carrier gas-hot extraction, and the relevance of various technological treatments (milling, heat treatment) on the oxygen concentration was evaluated.
Abstract: The oxygen content in the process of the production of oxide dispersion strengthened copper by mechanical alloying was traced by carrier gas-hot extraction. First, the usual determination of the total oxygen content was carried out. Second, the analytical method was checked and modified with respect to the selection and detection of different oxygen species in the sample. Applying this analytical approach the relevance of various technological treatments (milling, heat treatment) on the oxygen concentration was evaluated.
TL;DR: In this article, the particle morphology changes with variations in the C/(C+N) ratio of solid solutions formed in the system and the particle size becomes larger with an increase in the duration of sintering.
Abstract: TiC-TiN-Ni-(B) systems were investigated to understand particle coarsening and morphology changes as a function of sintering time and compositions. In addition, the variations in the C/(C+N) ratios of Ti(C1-xNx) solid solutions formed in the system were studied. As expected, the particle size becomes larger with an increase in the duration of sintering. However, added boron significantly reduced the growth of particles. X-ray diffraction analysis shows that the binder phase consists largely of Ni3B in TiC-TiN-20Ni-1B (in wt-%) system. The presence of boron in the liquid Ni seems to interfere with the dissolution of TiC and TiN and/or transport of Ti, C, and N. The effect of boron decreases as the amount of Ni binder increases. The particle morphology is found to change with variations in the C/(C+N) ratio.
TL;DR: In this paper, a composite metal powder mixture using molybdenum and copper powders was consolidated tonear theoretical density using the rapid consolidation technique of plasma pressure compaction, which is an essential requirement for better microstructural control and mechanical properties in the consolidated product.
Abstract: In this study, a composite metal powder mixture using molybdenum and copper powders was consolidated tonear theoretical density using the rapid consolidation technique of plasma pressure compaction. Rapid consolidation of the mixture of metal powders is an essential requirement for better microstructural control and mechanical properties in the consolidated product. The microstructure and hardness of the composite samples are compared with monolithic samples made by consolidating pure molybdenum powders under identical conditions. Microhardness measurements revealed an increase in hardness of molybdenum when mixed with small amounts of copper. The role of consolidation parameters on hardness and microstructural development is presented and discussed.
TL;DR: In this paper, a mixture of tungsten oxide and tungstic acid was collected at the anode with an overall recovery efficiency of about 90% and the microhardness of the consolidated sample was measured to be 2200 HV.
Abstract: WC-Co scrap generated by the cutting tool industries was electrochemically broken down to cobalt, which was deposited at the cathode and a mixture of tungsten oxide and tungstic acid was collected at the anode with an overall recovery efficiency of about 90%. The tungsten oxide/tungstic acid was reduced to produce nanostructural tungsten powders, which were subsequently carburised and chemically coated with cobalt to produce WC-Co powders. The powders synthesised were characterised for purity and size.The WC-Co powders, thus obtained were consolidated to near theoretical densities using a novel plasma pressure compaction (P2C) technique. The microhardness of the consolidated sample was measured to be 2200 HV, which is 20% higher than the reported literature values.