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In the present work, two powders of pure Al and of pure Mo, respectively, have been mixed (composition: Al with 15 at.% Mo) and processed by ball milling. The structural changes of the powder vs. milling time were analyzed by X ray diffraction and by scanning electron microscopy up to a milling time of 100 hours. The pitting potentials of the green and of the sintered alloy were determined in NaCl-solution. Experimental Methods MaterialsThe raw materials used in this work were elementary powders of aluminum and of molybdenum. The aluminum powder from Alcoa had a purity of 99.7% and the following particle size distribution: +100#: 0%, +200#: 0.1%, +325#: 11.5%, -325#: 88.4%, according to the manufacturer's analysis. The molybdenum powder from Aldrich had a purity of 99.9+% and an average particle size <10 µm (-100#). The two powders were mixed before milling and 1 wt.(%) of stearic acid was added as process controlling agent. Milling processMilling was performed in a ball mill type Netzsch Molinex PE5. The mill had a stainless steel rotator and chromium steel balls of 6 mm diameter. The ball to powder weight ratio was 10:1. The mill was water cooled and the chamber was purged with argon during the milling process. Milling was carried out with a velocity of 400 rpm. The milling process was interrupted several times in order to remove a small quantity of powder for analysis.A maximum milling time of 100 hours was considered as convenient. Zdujic et al. 8 reported that after this milling time, with low energy, molybdenum was finely dispersed in the aluminum matrix. IntroductionAluminum alloys are susceptible to pitting corrosion in chloride containing solutions. Massive pitting sets in when a critical potential, the so called pitting potential is reached. Alloying elements can influence this critical potential. However, among the alloying elements contained in technical alloys, only Cu shifts the pitting potential up to about 150 mV to the noble direction, but this is not enough to obtain a substantial improvement of the corrosion resistance. In the nineties researchers produced supersaturated Al alloys, mostly alloyed with transition elements such as Mo, W, Ta, Zr, Nb, Cr, Ni [1][2][3][4] . Also rare earth elements have been added more recently 5 . Since the solubility of these elements in Al is very low, they have to be produced by non-equilibrium methods like PVD, ion-implantation or meltspinning. Electrodeposition from ionic liquids has also been applied for supersaturated aluminum alloys 6 . Shifts of more than 1V were reported for the pitting potential of some alloys in chloride solution 1 . However, the drawback of these materials is that they can be produced only as deposited thin films or as thin ribbons, which does not permit their direct technical use. Although it is known that supersaturated alloys can also be produced by high energy ball milling 7 , until now the powder metallurgical way to corrosion resistant supersaturated aluminum alloys has not been examined. Therefore the aim of this paper is to st...

The present work reports a comparative study of cemented carbides of compositions WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni and WC-12Ni-6Co. The purpose was to study the powder metallurgical production process of these compositions starting from a commercial WC-6Co powder, obtaining the desired compositions by mass balance with pure Co and pure Ni powders. During the process steps mixing, milling, compacting and sintering the powders were described by its apparent density, green density, shrinkage and sintered density. Lower densities were observed in composites with higher binder content. The process was monitored by scanning electron microscopy and EDS analysis to evaluate the homogeneity of the powders, to detect contaminations by the process and to characterize the microstructure of the sintered materials. A finer microstructure was found when the binder contained Ni. Potentiodynamic polarization tests in sulfuric acid revealed pseudo-passive behavior for all the tested hard metals.

Building on theoretical and empirical insights and applying the thriving theory as the conceptual framework, the authors developed two new teacher-specific scales, namely the Teacher Stress Scale (TSS) and the Teacher Thriving Scale (TTS). The goal of this investigation was to evaluate the psychometric properties of these two scales. Data were collected through an online questionnaire administered to a national sample of 122 participating early childhood teachers (ages 22–72 years, M = 41.01) teaching in preschool through third grade in 26 states of the United States during the 2020–2021 school year amidst COVID-19. This study revealed some important psychometric results. First, with respect to their internal structures, both the TSS and the TTS appeared to be best represented as bifactorial and trifactorial, respectively. Specifically, the TSS comprised two constructs: (1) Inadequate School-based Support, and (2) Teaching-related Demands; and the TTS encompassed three constructs: (1) Adaptability and Flexibility, (2) Personal Strengths and Professional Growth, and (3) Positive Mindset. Second, the negative correlation between the TSS and the TTS provided discriminant evidence for each other’s construct validity, while the positive correlations between the TTS and six conceptually cognate constructs (Stress Resilience, Resilience Coping, Coping Efficacy, Teaching Satisfaction, Emotional Support, and Gratitude) demonstrated convergent evidence for construct validity for the TTS. Third, both the overall TSS and the overall TTS as well as their subscales exhibited good internal consistency reliability. Fourth, both the overall TSS and the overall TTS also demonstrated test–retest reliability.

Resumo AbstractO objetivo deste trabalho é realizar um estudo comparativo sobre a influência de lubrificantes no

Influência do bismuto nas propriedades mecânicas do aço rápido AISI M2 sinterizado Influence of the bismuth on mechanical properties of high speed steel AISI M2 sintered

Resumo AbstractPalavras-chave: metalurgia do pó, sinterização, parafusos ortodônticos.

Resumo AbstractOs metais duros constituem um grupo de materiais conhecidos como compósitos sinterizados que associam fases duras (carbetos), com uma fase metálica sendo amplamente utilizados em aplicações onde se deseja elevada dureza e resistência ao desgaste, aliada à alta tenacidade. Neste artigo apresentam-se os resultados da adição de 1% em peso dos elementos Nb, Ti, Cr e Mo na microestrutura do metal duro a partir de um compósito comercial de WC-6Co. A esse compósito foi adicionado 1,5% (em peso) de estearato de zinco como lubrificante e sinterizados na temperatura de 1450ºC numa atmosfera de Argônio. Com o objetivo de analisar-se a eficiência do produto, realizou-se a caracterização micro estrutural através dos ensaios de densidade à verde, contração volumétrica, densidade da sinterização, microestrutura e microdureza.Hard metals are a group of materials known as sintered composites involving hard phases (carbides) with a metallic phase, being widely used in applications where you want high hardness and wear resistance combined with high toughness. This article presents the results of adding 1% by weight of the elements Nb, Ti, Cr and Mo on the microstructure of the hard metal from a commercial composite of WC-6Co. In this composite was added 1.5% (by weight) of zinc stearate as lubricant and sintered at a temperature of 1450ºC in an atmosphere of argon. Aiming to analyze the product efficiency was held on micro structural characterization through the testing of green density, shrinkage, sintered density, microstructure and microhardness. Palavras-chave:metal duro, carbetos, balanceamento de massa, metalurgia do pó, sinterização.