Analysis of the influence of surface roughness of various types of wood on the results of their hardness measured by the Leeb method

Determining the hardness in the Leeb scale consists in measuring the velocity of the impact mass before and after hitting the sample. The result is the speed of the impactor shall after the rebound divided by the speed before the rebound (multiplied by 1000). The measured hardness ranges from 0 to 1000 and is largely dependent on the Young's modulus of elasticity. The article presents the Leeb hardness measurement tests of six various species of wood. The samples were machining before testing in such a way that there were places with different surface roughness on its surface. The research showed the differentiation of the hardness test results for the same tree species depending on the roughness of the surface

The homogenous alternative to biomineralization: Zn- and Mn-rich materials enable sharp organismal “tools” that reduce force requirements

We measured hardness, modulus of elasticity, and, for the first time, loss tangent, energy of fracture, abrasion resistance, and impact resistance of zinc- and manganese-enriched materials from fangs, stings and other “tools” of an ant, spider, scorpion and nereid worm. The mechanical properties of the Zn- and Mn-materials tended to cluster together between plain and biomineralized “tool” materials, with the hardness reaching, and most abrasion resistance values exceeding, those of calcified salmon teeth and crab claws. Atom probe tomography indicated that Zn was distributed homogeneously on a nanometer scale and likely bound as individual atoms to more than ¼ of the protein residues in ant mandibular teeth. This homogeneity appears to enable sharper, more precisely sculpted “tools” than materials with biomineral inclusions do, and also eliminates interfaces with the inclusions that could be susceptible to fracture. Based on contact mechanics and simplified models, we hypothesize that, relative to plain materials, the higher elastic modulus, hardness and abrasion resistance minimize temporary or permanent tool blunting, resulting in a roughly 2/3 reduction in the force, energy, and muscle mass required to initiate puncture of stiff materials, and even greater force reductions when the cumulative effects of abrasion are considered. We suggest that the sharpness-related force reductions lead to significant energy savings, and can also enable organisms, especially smaller ones, to puncture, cut, and grasp objects that would not be accessible with plain or biomineralized “tools”.

Pressing and Infiltration of Metal Matrix Nanocomposites

The ability to produce metal matrix nanocomposites via pressing and infiltration was validated. Al/TiC nanocomposite was used as the model material. Pressing the powder in a die yielded cylindrical specimens with a green density of 1.98 ± 0.05 g/cm3, which was increased to only 2.11 ± 0.12 g/cm3 by sintering. Direct infiltration of the pressed specimens at 1050 °C for 3.5 h yielded specimens with a density of 3.07 ± 0.08 g/cm3, an open porosity of 3.06 ± 1.40%, and an areal void fraction of 8.09 ± 2.67%. The TiC nanoparticles were verified to be well dispersed using energy-dispersive X-ray spectroscopy. The measured hardness of 64 ± 3 HRA makes it a promising material for structural applications in industries such as aerospace and automotive.

Influence of additives on suspension structure

The aim of this study was to compare the stability and texture of three zinc oxide suspensions with different additives. Suspension 1 was made as official magistral formulation Suspensio album 7.5% from Formulae magistrales 2008. Suspension 2 was prepared when 1% carbomer gel was added to suspension 1 and suspension 3 was prepared when polysorbate 20 was added to suspension 2. After stability tests, texture analysis was performed on all suspensions. Following parameters were measured: hardness cycle 1, hardness cycle 2, cohesiveness, adhesiveness, resilience and springiness. The study showed that suspension 3 had the lowest value of hardness, and therefore the best spreadability. Also, suspension 3 was the least sticky of all three, since it was characterized with the lowest adhesiveness. Further, suspension 3 was the most cohesive and is predicted to withstand the stress during packing and use longer than others. On the other hand, the highest values of resilience and springiness were detected for suspension 1, while the lowest was related to suspension 2. Therefore, the best textural characteristics were assigned to suspension 3. This result is in accordance with the results of performed stability tests. The results of our study offer insight into potential improvements of the current magistral formulation Suspensio album 7.5%.

Improving the uniformity of strength distribution in cylindrical specimens formed from iron based powders

The distribution of microhardness in cylindrical samples formed from industrial iron-based powders and not subjected to sintering is experimentally studied. This distribution is described by a simple mathematical model. It is shown that the measured hardness has a significant correlation with the strength. Microhardness is correlated with the local strength. Because, during the subsequent sintering and heat treatment of the powder sample, phase transformations occur within the individual grains, the microhardness distribution that occurs before the sample is sintered will remain after sintering. The technology of microhardness equalization in the sample at the stage of its forming, before sintering, is described.

Evaluation of Stationary Creep Rate in Heat-Affected Zone of Martensitic 9–12% Cr Steels

The purpose of the present study was to evaluate the contribution of distinct regions of the simulated heat-affected zone (HAZ) to the overall creep behavior of welded joints in the X20 and P91 steels. The HAZ was simulated by means of dilatometry at four peak temperatures (900, 1000, 1200, and 1350 °C) with a consequent tempering at 650 °C. Microstructure features of the four simulated HAZ regions including precipitates, prior austenite grains, and subgrains were quantified by means of electron microscopy. The quantified parameters and the measured hardness were used in three physical models for evaluation of the stationary creep rate (ε˙ at 170 MPa and 580 °C. The resulting ε˙ values fall within the range 10−8–10−7 s−1, being in good agreement with the experimental data with a similar thermal history, but an order of magnitude lower than the measured values for the parent metal of the studied steels (10−7–10−6 s−1). Depending on the model utilized, their output can be linearly related to hardness, subgrain size, or interparticle spacing. The model relating ε˙ to hardness was the most consistent one in prediction, being always lower for higher peak temperatures.

Effect of Cavitation Erosion Wear, Vibration Tumbling, and Heat Treatment on Additively Manufactured Surface Quality and Properties

The paper is devoted to researching various post-processing methods that affect surface quality, physical properties, and mechanical properties of laser additively manufactured steel parts. The samples made of two types of anticorrosion steels—20kH13 (DIN 1.4021, X20Cr13, AISI 420) and 12kH18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321) steels—of martensitic and austenitic class were subjected to cavitation abrasive finishing and vibration tumbling. The roughness parameter Ra was reduced by 4.2 times for the 20kH13 (X20Cr13) sample by cavitation-abrasive finishing when the roughness parameter Ra for 12kH18N9T (X10CrNiTi18-10) sample was reduced by 2.8 times by vibratory tumbling. The factors of cavitation-abrasive finishing were quantitatively evaluated and mathematically supported. The samples after low tempering at 240 °C in air, at 680 °C in oil, and annealing at 760 °C in air were compared with cast samples after quenching at 1030 °C and tempering at 240 °C in air, 680 °C in oil. It was shown that the strength characteristics increased by ~15% for 20kH13 (X20Cr13) steel and ~20% for 12kH18N9T (X10CrNiTi18-10) steel than for traditionally heat-treated cast samples. The wear resistance of 20kH13 (X20Cr13) steel during abrasive wear correlated with measured hardness and decreased with an increase in tempering temperatures.

Producing non-dendritic A356 and A380 feedstocks: Evaluation of the effects of cooling slope casting parameters

In this study, low superheat casting and cooling slope casting processes were carried out with A356 and A380 aluminum alloys in order to obtain feedstocks with near globular microstructures. Castings were conducted at 20 °C above of the liquidus temperature for both processes and molten alloys were cast through a copper cooling slope with two different lengths (350 mm and 650 mm) and two different tilt angles (30° and 60°). In order to evaluate the significance of boron nitride coating on cooling slope, castings in short slope were carried out under both coated and uncoated conditions. Microstructural examinations and hardness measurements were carried out. According to obtained results, cooling slope casting caused superior microstructural properties as compared to low superheat casting, especially for A356 alloy. 30° tilt angle was found more efficient in order to obtain a more globular microstructure for A356, while, on the other hand, the tilt angle of 60° was detected more favorable in that manner for A380. Obtained grain size measurements were slightly improved with the employment of short slope and coating was found beneficial especially for A356 alloy. The measured hardness values did not display any significant difference in the same alloy type except in the low superheat cast A356 specimen, which was obtained with coarser microstructure.

Soldering of 7075 Aluminum Alloy Using Ni-P and Cu-Cr Electrodeposited Interlayers

Direct soldering of the aluminum alloy 7075 is very difficult or even impossible. In order to make it possible, galvanic coatings and the procedures for their application on alloy surfaces were developed. The paper presents structures and mechanical properties of soldered joints of the 7075 alloy, made in indirect way with use of electrolytically deposited Ni-P and Cu-Cr coatings. Application of the newly developed Ni-P and Cu-Cr coatings on base surfaces of the 7075 alloy is described. The results of wettability examination of the S-Sn97Cu3 solder in the droplet test and by spreading on the coatings applied on the 7075 substrates are presented. The wettability angle of both coatings was lower than 30°. The results of metallographic examinations with use of light and electron microscopy are presented. It was shown that adhesion of metallic coatings to the aluminum alloy is good, exceeding shear strength of the S-Sn97Cu3 solder. Shear strength of soldered joint was equal to 35 ± 3 MPa. Measured hardness of the Ni-P interlayer reached high value of 471 HV 0.025.

Microstructure Observation and Nanoindentation Size Effect Characterization for Micron-/Nano-Grain TBCs

Microstructure observation and mechanical properties characterization for micron-/nano-grain thermal barrier coatings were investigated in this article. Scanning electron microscope images demonstrated that both micron-grain coating and nano-grain coating had micrometer-sized columnar grain structures; while the nano-grain coating had the initial nanostructures of the agglomerated powders reserved by the unmelted particles. The mechanical properties (hardness and modulus) of micron-/nano-grain coatings were characterized by using nanoindentation tests. The measurements indicated that the nano-grain coating possessed larger hardness and modulus than the micron-grain coating; which was related to the microstructure of coatings. Nanoindentation tests showed that the measured hardness increased strongly with the indent depth decreasing; which was frequently referred to as the size effect. The nanoindentation size effect of hardness for micron-/nano-grain coatings was effectively described by using the trans-scale mechanics theory. The modeling predictions were consistent with experimental measurements; keeping a reasonable selection of the material parameters.