Greater Hardness Research Articles

A genetic base of utilisation of maize cob as a valuable naturally renewable raw material

The original technological method of the maize cob processing has been developed at the Maize Research Institute, Zemun Polje, by which lignocellulose granules of different particle sizes are produced from the cob. Different chemical composition and physical and chemical properties of these fractions, and especially a great capacity of binding liquids particularly oil and water determine, their usage as degreasing and drying means. Due to their great hardness and abrasive capacity, products made from ground cobs are usable for polishing in the metal processing industry, while the composition of certain compounds (pento-san) are of a particular importance in the chemical industry for the pro duction of furfural and its derivates. As these products are inert, of neutral pH and free of heavy metals they are used as organic carriers in the pro duction of pesticides and agro-chemicals, as well as, in cosmetics and the pharmaceutical industry.

Solidification Processing and Fracture Behavior of RuAl-Based Alloys

ABSTRACTAlloys of RuAl-Ru were processed using various solidification methods, and the fracture behavior was examined. The fracture toughness values for RuAl-hcp(Ru, Mo) and RuAl-hcp(Ru, Cr) alloys ranged from 23 to 38 MPa√m, while the volume fraction of RuAl ranged from 22 to 56 percent. Increasing the volume fraction of RuAl resulted in a decrease in fracture toughness. The hcp solid solution was shown to be the more ductile phase with a fracture toughness approaching 68 MPa?m, while the B2 solid solution (RuAl) was found to have a fracture toughness less than 13 MPa√m. An alloy of Ru-7Al-38Cr (at.%) that consisted of a hcp matrix with RuAl precipitates had the highest room temperature toughness and the greatest hardness.

Comparative Study of Water Sorption and Solubility of Soft Lining Materials in the Different Solutions

In this study, two acrylic based materials and three silicone rubber soft lining materials were investigated to determine the percentage of absorption and solubility in artificial saliva, distilled water, and denture cleanser. In addition, the effect of denture cleanser on surface properties of soft lining materials was also evaluated. For sorption and solubility testing, 75 discs (50 mm x 0.5 mm) were prepared and divided into 5 groups with 15 samples in each group. The specimens were stored in different solutions, and tested after 1, 4, and 16 weeks. Analysis of variance was used to find the significant differences between the materials at all time intervals. The acrylic resin soft lining materials had higher solubility (3.432% Visco-gel in artificial saliva) and absorption (3.349% Visco-gel in distilled water) than Molloplast-B after 16 weeks of aging. The greatest hardness and color change were shown in the acrylic soft lining materials.

Pseudomorphic stabilization on crystal structure and mechanical properties of nanocomposite Ti-Al-N thin films

ABSTRACTAs the dimensions of materials are reduced to the nanometer scale, the stabilization of pseudomorphic crystal structures that differ from their bulk equilibrium phases can occur. The pseudomorphic growth could provide a substantially larger bulk modulus and greater hardness than the average of the constituent materials in nanolayered and nanocomposite thin films. To evaluate this effect in Ti1-xAlxN system, a series of nanostructured films with × up to 0.7 were deposited onto WC-Co substrates using arc PVD, and characterised in terms of structure-property relations. Chemical composition by RBS together with HRTEM and XRD analysis showed that for the Al content below × = 0.4 a solid solution single-phase film is formed, while for × values beyond 0.5 mixed structures made of fcc-TiN and hcp-AlN, or nanocomposite films made of fcc-TiN, hcp-AlN, and fcc-AlN appeared depending on deposition conditions. Hardness of solid solution films was found to increase almost linearly with the Al content, while two opposite behaviours were distinguished for composite structures. Hardness rapidly decreased according to the rule of mixture as soon as solid solution phase began to separate into TiN and AlN growing in their natural structures with misfit dislocation at the interface. In contrast, further hardness enhancement was measured when nanocomposites with coherent interfaces were formed due to pseudomorphic stabilization of fcc-AlN on fcc-TiN crystallites.

Investigation of antiwear coatings deposited by the pvd process

AbstractThe tribological properties of various PVD‐deposited coatings (vacuum arc method) have been tested, both single‐layer coatings (TiN, CrN, Ti(C,N), and Cr(C,N)) and multilayer coatings (Cr(C,N)/CrN/Cr and CR(C,N)/(CrN+Cr2N)/CrN/Cr). An unlubricated ball‐on‐disc tribosystem was used in which an Al2O3 ball is pressed against a coated steel disc rotating in the horizontal plane. A novelty of the method is the removal of wear debris from the contact zone using a draught of dry argon. This improves the repeatability of the test results and the stability of the tribological characteristics.It is shown that CrN coatings exhibit the best antiwear properties and Ti(C,N) the worst. Multilayer coatings have better antiwear properties than single‐layer ones. The friction coefficients for CrN and Cr(C,N) coatings are much smaller than for the commonly used TiN.A correlation has also been found between the physical properties of the coatings tested (adhesion of the coating to the substrate assessed in scratch tests, and coating hardness) and their antiwear properties. An improvement in coating‐substrate adhesion results in wear reduction, while greater hardness (causing a coating embrittlement increase and a change in the wear mechanism) brings about greater wear. There is no correlation between the physical properties and the friction coefficients of the coatings tested.

Oxidation, flavor, and texture of walnuts reduced in fat content by supercritical carbon dioxide

AbstractEnglish walnuts are popular because of their good taste, high n−3 FA content, and reported hypocholesterolemic effects. However, walnuts have a high fat content (∼70% w/w) that is highly polyunsaturated, which contributes to oxidative instability. The objectives of this study were: (i) to use supercritical carbon dioxide (SC‐CO2) extraction to decrease the total fat content of walnuts, and (ii) to determine the effects of SC‐CO2 lipid extraction on the oxidative stability, flavor, and textural characteristics of the reduced‐fat walnuts. The fat content of English walnut pieces was reduced by 25 and 40% with a pilot‐scale SC‐CO2 extraction system. Full‐fat, 25‐, and 40%‐reduced‐fat walnuts were stored at 25 and 40°C for 8 wk. FA profiles were similar for residual oil in all treatments, and the profiles did not change with storage. PV and volatile compounds were significantly greater (P<0.05) in full‐fat walnuts than in reduced‐fat walnuts at both storage temperatures. A trained sensory panel judged the reduced‐fat walnuts to be less astringent and to have less walnut and rancid flavors. Full‐fat walnuts had greater hardness than reduced‐fat walnuts by both sensory and instrumental texture profile analyses. In general, reducing the relative fat contents of walnuts by 25% improved oxidative stability and maintained a high level of consumer acceptance.

Structural and Mechanical Properties of Nanostructured Granular Alumina Catalysts

Granular gamma-Al2O3 support and 8 wt % CuO/gamma-Al2O3 catalyst were synthesized by a sol-gel granulation method. The pore structure, crush strength, hardness, and elasticity of these sol-gel-derived catalysts were studied and compared with similar commercial catalysts prepared by non-sol-gel methods. Alumina and CuO-coated alumina granular particles prepared by different methods have different macro- and microstructure. The sol-gel-derived granular gamma-alumina and CuO-coated gamma-alumina granular particles have a structure defined by compact packing of uniform, nanosized gamma-alumina crystallites. They are characterized by a more uniform pore size distribution and larger surface area as compared to similar commercial samples with a structure defined by packing of aggregates consisting of nonuniform gamma-alumina crystallites. Because of the differences in the macro- and microstructure, the sol-gel-derived granular samples offer higher crush strength and greater hardness than the commercial samples.

Electric Rolling of Powder Materials with a Dielectric Phase

The effect of dielectric phase content on the properties of powder matrix composites (Kh20N80‐2M, NPG‐80, Nibon‐20) prepared by electric-pulse sintering with rolling is studied. The change in properties is most pronounced in composites with a filler that has greater hardness than the matrix material. The highest specific electrical resistivity, ultimate tensile strength, and a reduction in hardness are achieved with identical volume fractions of components and the maximum exponent in the Joule component of electric current. Use of electric-pulse sintering with rolling makes it possible to prepare strips with a large fraction of nonforming phase, especially from high‐yield powders.

Durability of powder-coated hot-dip galvanized steel

In this study, the quality and durability of powder-coated hot-dip galvanized products have been investigated. Standard steel coupons hot-dip galvanized in conventional and delta (i.e., high temperature) conditions were coated with powder paint systems or a high quality solvent-based system and then subjected to a wide range of test methods representing mild or highly aggressive exposure conditions. Additional variables in the project were the silicon content of the steel and the treatment prior to painting. The use of delta-galvanized steel as a base for painting offers a number of advantages such as much greater hardness and improved paint adhesion. Maximum corrosion protection is observed if the galvanized base is treated with chromate and sequentially powder coated with an epoxy primer followed by a polyester topcoat.

Nitrogen ion irradiation of Au( [formula omitted]): formation of gold nitride

Often metal nitrides posses unique properties for applications, such as great hardness, high melting points, chemical stability, novel electrical and magnetic properties. One route to the formation of metal nitride films is through ion irradiation of metal surfaces. In this report, the results of irradiation of Au(1 1 0) surfaces by nitrogen ions with kinetic energies of 0.5 and 2 keV are studied with high resolution X-ray photoemission spectroscopy. N1s core level spectra show clear evidence for the formation of a gold nitride at, or in close vicinity to, the surface––the first direct observation of nitride formation by this element. Subsurface molecular nitrogen is also observed, the relative concentration of which increases with irradiation energy. We suggest that the subsurface molecular nitrogen is most likely present in the form of trapped bubbles.

Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part II. Electrostatic probe measurements

In an ongoing effort to investigate plasma plume features yielding high quality diamond-like carbon films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets. The advancing plasma plume produced by these structurally different targets are observed to possess quantitatively similar total heavy particle inventory, ionized fraction, and electron thermal content, yet quite different ion kinetic energy, plume profile, C2 formation mechanism, and concentration of complex molecules. Plume electron temperatures are observed to reside in the range 1–3 eV, with those in SCG plumes ∼10%–30% greater than a-C at all spatial positions downstream of the target. For both target cases, we find Te drop off with position away from the target with radiation as the most likely loss mechanism for these noninteracting plumes propagating in vacuum. Electron density is found to be ∼10%–12% lower near the target in SCG than a-C plumes consistent with mass loss inventory measurements, whereas ion fractions are estimated in the range ∼10%–15% for both target cases. All recorded data support the conclusion that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly comprised of C and C+ under vacuum conditions with the addition of C2 at high fill pressure. A significantly smaller profile peaking factor for SCG plumes supports this conclusion. Less energetic and slightly lower temperature SCG plume conditions are consistent with reduced peaking and more massive plume species. Plasma plumes from SCG targets exhibit laser energy (El) dependent peaking, again consistent with more complex molecules increasingly disassociated with El increase. The El dependence further suggests the potential for control of particle size distribution and plume profile peaking, though not independently. Consistent with this scenario is the observation of harder films produced from SCG targets at lower El. Micro-Raman results indicate strongly heterogeneous films deposited by SCG target ablation even under vacuum conditions further supporting the case for more complex structures with greater hardness. Energy balance estimates indicate that ion kinetic energy dominates the balance and that SCG ablation liberates about twice the number of C12 atoms from the target per unit El. As well, high pressure background fill indicates lesser plume energy attenuation for SCG plumes, again suggesting the presence of higher mass particles.

Effect of fat mimetics on physical, textural and sensory properties of cookies

Soft‐type cookies were prepared with up to 35% fat replacement by fat mimetics, namely Litesse (improved polydextrose), C*deLight MD 01970 (maltodextrins), Dairytrim (b‐glucans), pectin and Simplesse Dry 100 (a blend of micropatriculated whey proteins and emulsifiers). Physical, textural and sensory properties of the cookies were measured. All formulations with fat replacement up to 23% showed properties similar to control cookies except hardness. Cookies with 35% fat replacement by Litesse, a combination of Litesse and C*deLight MD 01970 and a combination of Litesse and Simplesse Dry 100 (50% each) presented a greater hardness, but physical properties as well as flavor and general acceptance comparable to the control cookies.

Microstructural analysis and crystallographic characterisation of plasma oxynitrided Ti–6Al–4V

Combined glow discharge oxidising and nitriding treatments allow the production on Ti–6Al–4V of modified surface layers with enhanced hardness properties compared with a traditional ion nitriding process. The treatment atmosphere has a marked influence on the properties of these hardened layers: as the oxygen concentration increases, thicker diffusion layers, characterised by greater hardness values and smoother gradients, are obtained. In the present paper the effects of treatment atmosphere and duration on the glow discharge oxynitriding of Ti–6Al–4V specimens are evaluated, by performing tests at 1173 K with oxygen concentration varied in the range 0–21 vol.-% and for treatment durations in the range 0·5–8 h. The modified layers produced consist of an outer compound layer and an inner diffusion layer. The compound layer consists of nitrides, oxides, and oxynitrides of titanium and, in some cases, of alloy element oxides too. With increasing oxygen concentration and/or time, the compound layer develops a stratified structure and its adhesion to the substrate becomes poor; this fact can be attributed to the high content of titanium oxide, TiO2 , in the layer. In the diffusion layer α-Ti crystals, rich in interstitial atoms, are present. The diffusion layers in the oxynitrided specimens are thicker and show higher hardness (up to 1300 HK) and smoother gradients than those produced by a traditional ion nitriding process under the same treatment conditions. Case depths of comparable thickness (around 45 μm) can be obtained by performing an 8 h nitriding treatment or a 2 h oxynitriding treatment with 6 vol.-%O2 . Moreover, α-Ti lattice parameters a, c were evaluated as a function of the experimental conditions; the values of these parameters can be correlated with changes in hardness values.

Synthesis and characterization of NbC whiskers

Niobium carbide, NbC, has a high melting point, great hardness, good chemical stability, good thermal conductivity and a low thermal-expansion coefficient. Because of these properties NbC whiskers are highly promising as reinforcing phase in ceramic matrix composites for cutting tool applications. In this article a carbothermal preparation route for NbC whiskers is presented. It is based on a vapor-liquidsolid (VLS) growth mechanism. The basic VLS mechanism involves vapor-phase transport of one or more of the reacting species to a melted catalyst droplet where the desired whisker is grown [1]. The metal catalyst must have a melting point or a eutectic point that is lower than the synthesis temperature—otherwise the VLS mechanism would not be operative. It must also be able to dissolve the whisker components, in this case Nb and C. Nickel has proved to be a good catalyst, and accordingly Ni(l) is known to solvate Nb and C [2]. In order to obtain a successful whisker growth, appropriate gas species have to be formed and transported to the catalyst at a sufficient rate. Equilibrium calculations with the program package HSC [3] show that niobium is transported in the vapor phase mainly as NbOCl3(g). According to our experience, obtained in preparing TiC, TiN1−x Cx , TaC, Tax Ti1−x C, and (Ta,Ti,Nb)C,N whiskers [4–7], the following reactions or very similar ones represent the actual mechanism when the reactions takes place in a flowing Ar atmosphere. Formation of Nb-containing gas species, using Cl as a volatilizing element

Precipitation sequence in friction stir weld of 6063 aluminum during aging

The precipitation sequence in friction stir weld of 6063 aluminum during postweld aging, associated with Vickers hardness profiles, has been examined by transmission electron microscopy. Friction stir welding produces a softened region in the weld, which is characterized by dissolution and growth of the precipitates. The precipitate-dissolved region contains a minimum hardness region in the aswelded condition. In the precipitate-dissolved region, postweld aging markedly increases the density of strengthening precipitates and leads to a large increase in hardness. On the other hand, aging forms few new precipitates in the precipitate-coarsened region, which shows a slight increase in hardness. The postweld aging at 443 K for 43.2 ks (12 hours) gives greater hardness in the overall weld than in the as-received base material and shifts the minimum hardness from the as-welded minimum hardness region to the precipitate-coarsened region. These hardness changes are consistent with the subsequent precipitation behavior during postweld aging. The postweld solution heat treatment (SHT) and aging achieve a high density of strengthening precipitates and bring a high hardness homogeneously in the overall weld.

Chrome Nitride Coatings for Applications in Plastics Processing

Abstract Coated moulds, especially cavity surfaces and ejection parts are state of the art in plastics processing. Regarding the plastification unit i.e. screws and barrels coatings are not well established. Wear in processing remains a problem, especially when no abrasion is permitted e.g. in manufacturing optical elements. The surfaces must resist the abrasion of hard glas fibres as well as the corrosive attack of the polymers. Electroplated chrome is one of the answers to these demands, because of its hardness and corrosion resistance. Another solution are thin hard coatings which are not yet well established. Titanium nitride produced by PVD technique was found to show excellent abrasion resistance but often not sufficient corrosion properties. Chrome nitride was found to have great hardness like TiN, corrosion resistance behaviour similar to electroplated chrome and in contrast to electroplated coatings no tensile internal stress. The present study deals with the spectrum of characteristic properties of CrxN coatings like hardness, adhesion, internal stress, chemical composition and phases produced by PVD magnetron sputtering. The coatings were deposited on steel, described in characteristics and tested in a model wear test with plasticized moulding material (PA 66-GF50 and others) simulating the tribological situation between screw and barrel of extruders or injection moulds. The tribological behaviour was studied after the complex test procedure. The high temperature of the plasticized material, high abrasion by glas fibres and corrosive influence could only change the coatings properties of CrxN slightly.

Experimental study of the laser quenching of 40CrNiMoA steel

Abstract The service life of the piston head and the stability of a large diesel engine are greatly affected by the wear resistance of the groove of the piston head. Conventional high-frequency quench-and-temper treatment results in several deleterious effects that may impair the anti-friction and wear properties of the groove of the piston head. Laser surface quenching is a new candidate technique. In this study, based on orthogonal experimental design, the effect of the surface condition, the laser power, the traverse speed, the incident angle and the gas flow rate on the quenched zone of 40CrNiMoA steel was investigated systematically. The profile, hardness and microstructure of the quenched zone vary with the surface condition, the laser power, the incident angle and the traverse speed. However, they are not significantly affected by the gas flow rate. The optimum processing parameters are obtained for the laser quenching of the groove of the piston head. Using the optimum processing parameters, quenched zones with not only sufficient case depth and greater hardness but also of a suitable profile and a finer microstructure, are obtainable. The hardness of the laser quenched zone is substantially higher than that resulting from conventional high-frequency quench-and-temper treatment.

Synthesis and mechanical/magnetic properties of nano-grained iron-oxides prepared with an inert gas condensation and pulse electric current sintering process

Nanocrystalline iron-oxide powder was fabricated with an inert gas condensation (IGC) method combined with evaporation, and in-situ oxidation techniques. The particle size of iron-oxide powder was controlled by varying the helium gas pressure between 0.1 and 10 Torr, with the smallest one =10 nm at 0.1 Torr. The nanostructure was characterized by TEM. Nanocrystalline iron-oxide powder was sintered with the pulse electric current sintering (PECS) method to obtain densified γ-Fe2O3 materials, and suitably densified nano-grained γ-Fe2O3 materials (≈ 40 nm) of great hardness were obtained. The correlation between the nanostructure and magnetic properties of nanocrystalline powder and densified γ-Fe2O3 materials was also investigated.

UDDEHOLM AISI D2

Abstract Uddeholm AISI D2 is a high-carbon, high-chromium, air-hardening tool and die steel capable of great hardness and high resistance to abrasive wear. It is nondeforming and is also somewhat corrosion resistant. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on heat treating, machining, and joining. Filing Code: TS-567. Producer or source: Uddeholm Tooling AB.

Brass-matrix silicon carbide whisker composites prepared by powder metallurgy

Brass (Cu-18Zn)-matrix and copper-matrix composites containing 0–50 vol% silicon carbide whiskers were fabricated by powder metallurgy using both the admixture method and the coated filler method, such that the fabrication of the copper-matrix composites did not involve a liquid phase whereas that of the brass-matrix composites did during the sintering process. The coated filler method gave composites with lower porosity, greater hardness, higher compressive yield strength, lower coefficient of thermal expansion (CTE), higher thermal conductivity and lower electrical resistivity than the admixture method, though the differences were much larger for copper-matrix composites than brass-matrix composites due to the liquid phase present during the fabrication of the brass-matrix composites. The mechanical properties of the brass-matrix composites were similar to those of the copper-matrix composites (also made by the coated filler method) at >35 vol% SiC, but were superior to those of the copper-matrix composites at 35 vol% SiC. The thermal conductivity was lower and the electrical resistivity was higher in brass-matrix composites than copper-matrix composites at <50 vol% SiC.