Pressed Samples Research Articles

Development of highly wear resistant Cu - Al alloys processed via powder metallurgy

Abstract The present work explores the effect of aluminium (Al: 0, 3, 5, 10 & 15 wt%) addition on wear behaviour of copper (Cu). The Cu-Al alloys were fabricated via mechanical alloying and high-pressure hot press. In fact, high-pressure processes are beneficial as they result in obtaining fine microstructure and property enhancement. Depending on the amount of Al, the microstructure of hot pressed samples (Cu with Al up to 5 wt%) consisted of copper-rich solid solution phase (Cu0.92Al0.08) and the presence of both Cu0.78Al0.22 and Cu9Al4 intermetallic phases for Cu containing high amount of Al (≥10 wt%). The relative density of Cu-Al alloys varied between ∼95 and 98% and the hardness of Cu enhanced significantly from 1.32 to 6.16 GPa with Al content. The coefficient of friction (COF) (0.54 to 0.16) and wear rate (18.26 × 10−5 to 0.92 × 10−5 mm3/N-m) of Cu decreased with the addition of Al. A transition in wear mechanisms of Cu was observed with Al. In case of pure copper, adhesion was the major wear mechanism. Adhesion and tribo-oxidation controlled the wear of Cu alloyed with Al (up to 5 wt%). Oxide layer formation influenced the wear of Cu-10Al, while abrasion was the predominant wear mechanism for Cu-15Al. These results clearly indicate the advantage of large amount of Al addition to achieve better wear resistance of Cu.

Non‐GAAP Earnings and the Earnings Quality Trade‐off

Using a large sample of earnings press releases by Australian firms, we compare multiple attributes of non‐GAAP earnings measures with their closest GAAP equivalent. We find that, on average, non‐GAAP earnings are more persistent, smoother, more value relevant, and have higher predictive power than their closest GAAP equivalent. However, the same set of non‐GAAP earnings disclosures are also less conservative and less timely than their closest GAAP equivalent. The results are consistent with non‐GAAP earnings measures reflecting a reversal of the trade‐off between the valuation and stewardship roles of accounting inherent in accounting standards and the way they are applied. We also find that differences in several of these attributes between GAAP and non‐GAAP earnings are more evident in larger firms, firms with lower market‐to‐book ratios, firms with a higher proportion of independent directors, and firms that report profits rather than losses. Our evidence is consistent with the argument that accounting standards impose significant amounts of conditional conservatism at some cost to the valuation role of accounting information. Non‐GAAP earnings measures can therefore be seen as a response to the challenges faced by a single GAAP performance measure in satisfying the competing demands of value relevance and stewardship.

Structural integrity of ultrafine grain Al-3%Mg alloy under dynamic loading conditions

Utilization of various materials for constructing dynamic components and equipments has increased ever today. The high speed deformation mechanics was studied in various scale levels, especially in micro and nano scales. Understanding the micromechanics using shock waves led to development of armor plates in military technology. One dimensional elastic stress is applied using Split Hopkinson pressure bar for the ultra-fine grain aluminum samples and microstructural evolution was discussed in detail. The material characterization of equi channel pressing and its effect on stability of material after shock wave testing is provided. The grain size of material is steadily decreased to obtain ultra-fine grain structure during equi channel pressing and by application of shock waves on those pressed samples, the grain size again increases within the material. The recovery, re-crystallization and grain growth was observed in those shock tested samples due to induced temperature during such shock testing. The existing dislocation sub structure in pressed samples devoid after inertia effects. It is proposed further to understand the interaction between precipitate particle and dislocations.

Microstructure-property relations of biphasic calcium phosphate obtained by hot pressing process

Biphasic calcium phosphate (BCP) was fabricated through hot pressing process from hydroxyapatite (HA) starting powder synthesized by a peroxide-based precipitation method and dried at 250?C. The synthesized HA powder contained some calcium hydrogen phosphate (CHP) as a minor phase. In this work, the dense BCP ceramics with a mixture of HA and ?-TCP phases were successfully obtained by hot pressing at temperature ranging from 700-1100?C. The amount of HA phase in the hot pressed samples decreased with increasing sintering temperature from 700 to 900?C, while the amount of ?-TCP exhibited an opposite trend. The relations between the microstructure and mechanical properties of the dense BCP ceramics sintered in the temperature range 700-1100?C were investigated. The sample hot pressed at 800?C has a dense structure with the highest hardness (4.86 ? 0.19GPa) and the lowest fracture toughness (0.80 ? 0.01MPa?m1/2). In addition, biocompatibility of apatite layer formed after immersion in simulated body fluid (SBF) for 14 days can be observed by SEM images. The results revealed that the samples hot-pressed at 800 and 900?C were covered by calcium phosphate (CaP) crystal layer indicating the strong interaction of BCP ceramics and SBF.

ENHANCEMENT OF MICROSTRUCTURE AND THERMAL EXPANSION COEFFICIENT OF AL/NI-SIC COMPOSITE PREPARED BY POWDER METALLURGY TECHNIQUE

Al/Ni-SiC composite was prepared via powder metallurgy technique, in which SiC particles were mixed with 10 wt % nickel powder for 24 hrs, then mixed by three percents 5, 10 and 15 wt.% with Al powder in a ball mill for 5 hrs. Three types of sintering techniques were used to prepare the composite. Uniaxial cold compacted samples were sintered in a vacuum furnace at 600oC for 1 hr. The second group was the vacuum sintered samples which were post-processed by hot isostatic press (HIP) at 600oC for 1hr under 190 MPa pressure. The third one was the hot pressed samples that were consolidated at 550oC under the uniaxial pressure of 840 MPa. The results showed that the hot compacted samples have the highest densification values (97-100%), followed by the HIP samples (94-98%), then the vacuum sintered ones (91-97%). The XRD analysis indicated the presence of peaks correspond to Al and Ni, also Al3Ni intermetallic and Al4Si2C5 phases which indicated that all SiC particles were consumed with Al particles to form Al4Si2C5. Hardness results revealed that hot compacted samples have the highest hardness values. Also the CTE results referred the decreasing of its value by increasing Ni/SiC percent.

Creating A Critical Civic Consciousness

This paper examines two themes in local government reporting in the nineteenth century—municipal governance and social reform and the reporting of municipal elections, electioneering and scandals. These themes formed part of the discourse of political reporting during this period, along with the detailed recording of town council meetings. The study concentrates on a representative sample of the provincial press in England from the Leeds Mercury to the Norfolk Chronicle. The article deliberately avoids an over-emphasis on the metropolitan press in an attempt to gauge the spread and influence of local government reporting outside of London. It also focuses on municipal political affairs and not on other forms of local government such as Poor Law Guardians, Improvement Commissioners and School Boards for the sake of clarity and unambiguity. Some writers have presented the provincial press as functioning as positive promoters of civic institutions and as underpinning the ‘municipal status quo’ [Jackson, Andrew. ‘Civic Identity, Municipal Governance and Provincial Newspapers: The Lincoln of Bernard Gilbert, Poet, Critic and “Booster”, 1914.’ Urban History 42 (2015): 113–129]. This study challenges this view and offers an alternative perspective—the creation of a critical civic consciousness that directly addressed the reader as a member of a critical urban community.

A study on the thermal and mechanical properties of composites made of nanolignocellulose and Pebax®polymer

This study aimed at producing the biodegradable composite from lignocellulose nanofibers (LCNFs) and Pebax®thermoplastic elastomer. For this purpose, LCNFs at different levels of 0, 1, 3, and 5% were considered. The LCNFs were prepared by benzyl alcohol and then mixed with Pebax®. The liquid phase of the LCNFs and soluble polymer was prepared and then the masterbatches were mixed in an internal mixer (Model 815802, Brabender, Germany). The mixtures from the internal mixer were put into a hot press and test samples were compress-molded. The physical properties results indicated that water absorption and thickness swelling decreased by the addition of more amount of LCNF. By the addition of LCNFs to polymer, the tensile strength and modulus and impact strength were increased compared to samples without LCNF. No regular trend of enthalpy changes was observed as the content of LCNF changed. When the LCNF concentration was increased to 5%, the crystallization temperature was increased. As the LCNF concentration increased to 3%, the glass transition temperature ( Tg) was decreased, whereas by incorporating more LCNFs, the Tgwas increased. The result of the Fourier transform infrared spectra showed the peaks at 1740 cm−1which indicated the presence of polyamide bonds. Also, new peaks were observed in the range of 1400–1500 cm−1that was probably related to the presence of C−C bonds of glucose at LCNFs chains.

A comparative study of oxygen pick-up of TiHDH powder during press and sinter and loose sintering processing

Press and sinter is considered to be the most cost effective powder metallurgy process for producing parts. However, loose powder sintering shows to be a more promising cost effective powder metallurgy process as it entails pouring powder into a mould followed by sintering. The differences in their behaviour with respect to densification, maintaining dimensional stability and their oxidation behaviours determine the choice of their industrial applicability. Titanium has a high affinity for oxygen which in turn makes it difficult to process components from powder. It also affects the mechanical properties of products significantly; particularly in applications where ductility is imperative. The focus of this study was therefore to evaluate the oxygen pick-up of the two cost effective powder metallurgy processes (press and sinter and loose sintering). A 100 Mesh TiHDH powder was used for sintering. Sintering was performed at 1500 °C for 4 hours. The oxygen contents of the green and sintered compacts were then compared. High oxygen contents were observed in tap density powder and pressed samples. The loosely sintered components showed high oxygen pick-up after sintering while oxygen pick-up decreased with increasing pressure in pressed samples. These results show that press and sinter is advantageous over loose sintering where oxygen control is critical.

Direct SPD-processing to achieve high-ZT skutterudites

For mass fabrication of thermoelectric generators a fast, cheap and simple method is required to produce high ZT leg material. It is well known that severe plastic deformation (SPD) enhances the density of defects and dislocations, and also refines the grains to nano-size. These are the essential key parameters for low thermal phonon conductivity. Consequently and as a first example, SPD via high-pressure torsion (HPT) at elevated temperatures in protective gas atmosphere was used to directly consolidate and plastically deform commercial p-type skutterudite powder, DDyFe3CoSb12, (DD stands for didymium) into a dense thermoelectric solid. The HPT-sample exhibited a high figure of merit, ZT > 1.3 at 773 K, much higher than that of the hot-pressed reference sample (HP) from the same powder. The ZT achieved is comparable with ZTs of corresponding high energy ball milled and hot pressed samples (HBM-HP) as well as of ball milled, hot pressed plus HPT processed skutterudites (BM-HP-HPT). The thermoelectric efficiency is even 4% higher. Synchrotron measurements were performed at temperatures from 300 to 825 K in order to evaluate the changes in grain size and dislocation density of the CP-HPT samples before, during and after annealing. SEM and TEM images served to give a better insight into the temperature dependent diversification of the new material. Due to grain refinement and enhanced dislocation density, the CP-HPT material exhibits higher hardness values than the reference sample. The elastic moduli are, within the error bar, the same.With large high-pressure torsion facilities at hand, a new, fast and therefore cheap mass production of thermoelectric leg material directly from powders can be envisaged. This new production technique furthermore warrants high figures of merit but excludes time-consuming ball milling and hot-pressing steps.

Features of the structure and macro responses in hard ferro piezoceramics based on the PZT system

The structure, microstructure, dielectric and piezoelectric properties of two ferroelectric materials based on the modified PbTiO3-PbZrO3 (PZT) system, prepared using the conventional ceramic technology and hot pressing method have been studied, and correlations among their elemental composition, phase constitution, grain structure and macro responses have been investigated. Specific features of ferroelectric-paraelectric phase transitions during the variation of the frequency of an alternating electric field (in the interval of 25 Hz ÷ 2 MHz) have been singled out. It was shown that the properties of samples produced without an externally applied pressure are not lower than those of the hot pressed samples thus allowing their perspective use in frequency-selective devices such as variable bandwidth filters.

Effect of Hot Isostatic Pressing and Powder Feedstock on Porosity, Microstructure, and Mechanical Properties of Selective Laser Melted AlSi10Mg

AlSi10Mg tensile bars were additively manufactured using the powder-bed selective laser melting process. Samples were subjected to stress relief annealing and hot isostatic pressing. Tensile samples built using fresh, stored, and reused powder feedstock were characterized for microstructure, porosity, and mechanical properties. Fresh powder exhibited the best mechanical properties and lowest porosity while stored and reused powder exhibited inferior mechanical properties and higher porosity. The microstructure of stress relieved samples was fine and exhibited (001) texture in the z-build direction. Microstructure for hot isostatic pressed samples was coarsened with fainter (001) texture. To investigate surface and interior defects, scanning electron microscopy, optical fractography, and laser scanning microscopy techniques were employed. Hot isostatic pressing eliminated internal pores and reduced the size of surface porosity associated with the selective laser melting process. Hot isostatic pressing tended to increase ductility at the expense of decreasing strength. However, scatter in ductility of hot isostatic pressed parts suggests that the presence of unclosed surface porosity facilitated fracture with crack propagation inward from the surface of the part.

Spark plasma sintering and hot pressing of ZTA-NbC materials – A comparison of mechanical and electrical properties

Zirconia toughened alumina can be made electrically conductive and thus electric discharge machinable by addition of a percolating dispersion of niobium carbide. In order to boost the productivity of the sintering process spark plasma sintering was tested at identical temperature and pressure but shorter dwell than in hot pressing. SPS sintering parameters for ZTA-NbC are developed and spark plasma sintered ceramics are compared to the hot pressed benchmark.During SPS a percolating NbC backbone of niobium carbide grains is formed which enhances electrical conductivity but impedes densification. Identical strength at however higher sintering temperature is achieved by SPS but the fracture resistance and hardness were always superior in hot pressed samples. The monoclinic content of zirconia grains in as fired SPS samples is higher despite smaller average grain size and the transformation toughening effect is less pronounced. SPS promises economic benefits due to shorter dwell and cooling cycles.

Mechanical properties of PLA-based composites for fused deposition modeling technology

To predict the mechanical behavior of 3D printed products, it is important to understand the composite material properties and the effect that parameters of 3D printing process have on the properties of these materials. The mechanical properties of PLA-based composite materials were studied in this work. The mechanical properties of the hot pressed samples were compared to those of the 3D printed samples. The elongation at break and the yield strength of the samples fabricated by 3D printing are decreased by 15–60% compared to those for the hot pressed samples. It has been found that the mechanical properties of 3D printed samples do not practically depending on the deposition scheme.

Effect of consolidation techniques on the properties of Al matrix composite reinforced with nano Ni-coated SiC

Abstract Al /Ni-SiC composite was prepared via powder metallurgy technique. SiC particles were coated with 10 wt% nano nickel by electroless deposition, then mixed by three percents (5, 10 and 15 wt%) with Al powder in a ball mill using 10:1 ball to powder ratio for 5 h. Three types of sintering techniques were used to prepare the composite. Uniaxial cold compacted samples were sintered in a vacuum furnace at 600 °C for 1 h. The second group was the vacuum sintered samples which were post-processed by hot isostatic press (HIP) at 600 °C for 1hr under the pressure of 190 MPa. The third group was the hot pressed samples that were consolidated at 550 °C under the uniaxial pressure of 840 MPa. The results showed that the hot pressed samples have the highest densification values (97–100%), followed by the HIP samples (94–98%), then come the vacuum sintered ones (92–96%). X-ray diffraction analysis (XRD) indicated the presence of Al and Al3Ni, which means that all SiC particles were encapsulated with nickel as short peaks for SiC were observed. Hardness results revealed that HIP samples have the highest hardness values. The magnetization properties were improved by increasing SiC/Ni percent, and HIP samples showed the highest magnetization parameter values.

A preliminary validation study of PuO2 incorporation into zirconolite glass-ceramics

Abstract:Zirconolite glass-ceramics are being developed as potential wasteforms for the disposition of Pu wastes in the UK. Previous studies utilised a variety of surrogates whilst this work uses both cold-press and sinter and hot isostatic press methods to validate the wasteform with PuO2. A cold press and sinter sample was fabricated as part of a validation study for plutonium incorporation in hot isostatically pressed (HIPed) wasteforms. The results confirmed the cold-press and sinter, achieved successful waste incorporation and a microstructure and phase assemblage that was in agreement with those expected of a HIPed equivalent. A HIP sample was fabricated of the same composition and characterised by SEM and XRD. Results were in agreement with the sintered sample and achieved complete waste incorporation into the glass-ceramic wasteform. These samples have demonstrated successful incorporation of PuO2 into glass-ceramic HIPed wasteforms proposed for processing Pu-based waste-streams in the UK.

Non-GAAP Earnings and the Earnings Quality Trade-off

Using a large sample of earnings press releases by Australian firms, we compare multiple attributes of non‐GAAP earnings measures with their closest GAAP equivalent. We find that, on average, non‐GAAP earnings are more persistent, smoother, more value relevant, and have higher predictive power than their closest GAAP equivalent. However, the same set of non‐GAAP earnings disclosures are also less conservative and less timely than their closest GAAP equivalent. The results are consistent with non‐GAAP earnings measures reflecting a reversal of the trade‐off between the valuation and stewardship roles of accounting inherent in accounting standards and the way they are applied. We also find that differences in several of these attributes between GAAP and non‐GAAP earnings are more evident in larger firms, firms with lower market‐to‐book ratios, firms with a higher proportion of independent directors, and firms that report profits rather than losses. Our evidence is consistent with the argument that accounting standards impose significant amounts of conditional conservatism at some cost to the valuation role of accounting information. Non‐GAAP earnings measures can therefore be seen as a response to the challenges faced by a single GAAP performance measure in satisfying the competing demands of value relevance and stewardship.

Wire EDM of ZTA-NbC Dispersion Ceramics – The Influence of ED Machining on Mechanical Properties

Zirconia toughened alumina (ZTA) ceramics are well known for their good mechanical properties such as high hardness and bending strength and moderate fracture resistance. By adding an electrically conductive phase, such as a transition metal carbide, ceramics can be machined by electrical discharge machining (EDM).In this study the influence of electrical discharge machining on the mechanical properties of ZTA-NbC was investigated. Hot pressed samples were wire electrical discharge machined to obtain bending bars for mechanical characterization. Machining included the main cut and four subsequent trimming operations. Machined and polished samples were characterized with respect to bending strength and Weibull modulus to elaborate the influence of the individual machining steps on strength reliability of the material. Moreover surface morphology and surface roughness of the machined samples were studied by SEM and white light interferometry.It was found out that the ED machining affects the average values of bending strength and the scattering of the data described by the Weibull Modulus. While Weibull modulus and thereby reliability evidently rises with increasing number and refinement of machining operations, while bending strength showed an intermediate strength minimum after the 1st trimming operation. Subsequent trimming steps partly recover the bending strength.

A comparative evaluation of the additional impact of nanometer-sized tetravalent oxides on the performance of Doloma-Magnesia ceramic refractories

In this research study, a comparative evaluation of the additional impact of nanometer-sized tetravalent oxides [Zirconia (ZrO2), Titania (TiO2), and Silica (SiO2)] on the properties and performance of Doloma-Magnesia (MgO-CaO) ceramic refractories, with an emphasis on their hydration resistance improvement, has been done. For this purpose, from 0 to 2.5wt% ZrO2, TiO2, and SiO2 nanometer-sized particles have been added to the Doloma-Magnesia compositions. After formulation and mixing of the starting materials, the pressed samples (at 150MPa) were tempered (at 250°C for 12h) and fired in a shuttle furnace (at 1650°C for 3h). The physical, mechanical, and thermo-mechanical properties of the fired samples have been investigated. Also, in order to detect the created crystalline phases and microstructure evaluation of the fired specimens, the XRD and SEM/EDS analysis have been used. The results showed that the use of silica, as well as zirconium and titanium nanometer-sized particles, have improved the sintering process via the liquid and solid state firing process mechanism, respectively. Also, the hydration resistance improvement order of the samples containing various nanometer-sized oxides is as ZrO2 > TiO2 > SiO2. Finally, in order to obtain the highest values of physical, mechanical and thermo-mechanical properties, the optimum content of each nanometer-sized tetravalent oxides was determined as ZrO2 = 2.5, TiO2 = 2.5, and SiO2 = 1wt%.

Improved Thermoelectric Properties in Melt-Spun SnTe.

SnTe has been the focus of numerous experimental and theoretical studies over the last years owing to its high thermoelectric performances near 800 K when appropriately doped. Here, we demonstrate that melt-spinning, an ultrafast-quenching synthesis technique, followed by spark plasma sintering results in enhanced ZT values in polycrystalline SnTe. To illustrate the impact of this technique, the results are contrasted with those obtained on two polycrystalline samples prepared by direct quenching of molten SnTe and without quenching. SnTe melt-spun ribbons are characterized by a peculiar columnar microstructure that contributes to lower the lattice thermal conductivity below 700 K in pressed samples. More importantly, this technique results in a significant decrease in the hole concentration, giving rise to enhanced thermopower values above 500 K. The variation in the hole concentration is likely due to a slight loss of elemental Te during the melt-spinning process. Thanks to the decreased hole concentration, the thermoelectric performances are significantly enhanced with a peak ZT value of 0.6 at 800 K, which represents a 40% increase over the values measured for samples prepared with and without quenching. These findings indicate that melt-spinning provides a novel strategy to improve the thermoelectric properties of SnTe that could be worthwhile extending to substituted compounds.

Effect of heat treatment on morphology and dielectric properties of PE cable insulation material

It is known that the heat treatment process in theproduction of extruded cables, affects the electricalproperties of polymeric insulation materials; this effectis via two main phenomena; first, it leads to diffusionand removal of polar substances from the system;second, it affects the polymer morphology by increasingthe polymer chain relaxation and creation of crystallites,hence increasing the crystallinity of the material.In this study, thick pressed samples with additive freelow density polyethylene (LDPE) insulation materialwere heat treated at different conditions for differentperiods of times. Differential scanning calorimetry(DSC) measurements confirmed that heat treatmentleads to higher crystallinity and higher lamella thicknessin LDPE. Dielectric properties of the material wasstudied by conduction current measurement anddielectric spectroscopy.Conduction current of samples with different heattreatment times was measured at high electric fieldswhich shows that the conduction current of LDPE isaffected by heat treatment. Generally, the apparentconductivity decreases by heat treatment.Dielectric spectroscopy measurements show that heattreatment does not have a significant effect on real andimaginary permittivity of the polymer. Interestingly, anincrease in the sample thickness via heat treatment, wasobserved both by sample thickness related to thememory effects in the polymer which needs to be takeninto consideration for accurate capacitancemeasurements.