Pd-Cu-Ni-P Bulk Metallic Glass: A Very Low Damping Material

The present work addresses damping experiments performed in a Pd-Cu-Ni-P bulk metallic glass. After an appropriated thermal treatment, this material exhibits a very low damping coefficient, down to 10⁻⁶. This result is discussed considering the different possible origins of the damping phenomena: thermoelasticity, energy dissipation by electrons, phonons, defects, and residual stresses. Thermoelasticity and defects appear to be the most important sources of mechanical damping. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25−March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Cooling Slope Casting Process for Synthesis of Bulk Metallic Glass Based Composites with Semisolid Structure

A process combining cooling slope casting and suction casting was developed to generate a semisolid structure in a Zr-based bulk metallic glass matrix composite. The melt was injected onto a cooling slope and subsequently vacuum sucked into a cylindrical copper mold placed at the end of the slope. The structure obtained for 4-mm-diameter specimens of composition Zr_66.4Nb_6.4Cu_10.5Ni_8.7Al₈ consists of a dispersion of spheroidal and rosettelike bcc crystals in a glassy matrix. Various slope angles, slope lengths, and injection pressures were tested. The coarsest and most spheroidal crystal structure was obtained at short slope lengths and high injection pressures. Microstructure analysis suggests that the slope is the location of extensive crystal nucleation and possible fragmentation, while the microstructure’s morphological evolution seems to occur mainly in the mold. The semisolid structure is expected to confer improved mechanical properties and ductility to the composite material.     

Fabrication of an In Situ Bulk Metallic Glass Composite with High Magnesium Content

In this work, an in situ bulk metallic glass composite in the Mg-Ni-Gd ternary system with high Mg content (>80 at. pct) that contains a ductile Mg-rich crystalline phase was produced by copper mold casting. The stability and devitrification process of the amorphous matrix in the composite structure have been studied using scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. The precipitation of crystalline phases from the amorphous matrix and the volume fraction of these phases were found to be dependent on both cooling rate and melt composition.     

A Novel Approach to Analysis of Complex Crystallization Behavior in Zr-Based Bulk Metallic Glass by Non-isothermal Kinetics Studies

Metallurgical and Materials Transactions A - The complex crystallization behavior of the Zr40Ti15Cu10Ni10Be25 bulk metallic glass (BMG) produced by suction-casting method was studied with the...     

Effects of Cooling Rates on Glass Formation and Magnetic Behavior for the Fe73.0C7.0Si3.3B5.0P8.7Mo3.0 Bulk Metallic Glass

In this paper, effects of cooling rates on glass formation and magnetic behavior of the Fe_73.0C_7.0Si_3.3B_5.0P_8.7Mo_3.0 (at. pct) alloy were investigated via different purging gases (i.e., helium and argon) during suction casting. X-ray diffraction patterns and transmission electron microscopy characterization confirmed that the maximum attainable diameter for glass formation is increased from 5 to 7 mm with the helium as the purging gas, relative to the argon. Meanwhile, the coercivity value (H _c) of the sample cast in helium is almost 5 times larger than that fabricated in argon, although the magnetization saturation in these two alloys is similar. Our pair distribution function analysis, density, and positron annihilation lifetime spectroscopy measurements indicated that the sample cast in helium possesses more free volume; however, the difference between them is insubstantial. Further, experimental results revealed that the residual stress in the samples cast under helium is much larger than that in those prepared in Argon, which could be responsible for the abrupt change in the coercivity.     

Strength of 444 Stainless Steel Single-Lap Joints Brazed with Ni-Based Metallic Glass Foils for Corrosive Environments

The tensile strengths, σ_SLJ, of 444 stainless steel single-lap joints (SLJs) brazed with two corrosion-resistant Ni-based braze filler metals (BFMs) were investigated and compared with results from joints made from 316L stainless steel using identical BFMs and processes. In previous work, we proposed that σ_SLJ could be understood in terms of SLJ geometry (primarily the ratio of overlap length o to plate thickness t—which determines the stress state), base metal properties (which determine stress state evolution with load), and braze microstructure (which determines local failure stress). The geometry and braze microstructure were varied in the prior work. The present study shows the effect of the base metal. 444 has higher yield stress, lower ultimate strength, and less strain hardening than 316L, and also experiences significant grain growth above 1100 °C. Although the braze microstructures of SLJs made using 444 are very similar to those of their 316L counterparts, not only σ_SLJ, but also variations of both σ_SLJ and failure mode with o/t are very different. Differences are not simply due to ultimate strength as is commonly assumed, but to how plasticity controls joint rotation and thus stress state during loading, as well as through-thickness grain boundaries acting as failure sites.

     

Strength of 316L Stainless Steel Single-Lap Joints Brazed with Ni-Based Metallic Glass Foils for Corrosive Environments

In brazing, the choice of base metal, brazing filler metal (BFM), and braze process conditions involves complex tradeoffs among cost, mechanical strength, corrosion resistance, and others. In this work, the tradeoff between strength and corrosion resistance of 316L stainless steel joints brazed with a newer “very corrosion-resistant” Ni-Cr-P-Mo-Si BFM and a more established “corrosion-resistant” Ni-Cr-Si-B BFM is quantitatively analyzed. Corrosion tests and microstructural analyses were performed using common practices. Joint strength was evaluated by testing brazed single-lap joints (SLJs) in tension following standardized procedures. However, conventional interpretations were found to be inadequate for quantitative comparisons. Therefore, the SLJ stress state was analyzed in detail and a complete interpretation was developed. Joint strength is shown to be determined by the SLJ geometry, base metal properties, and braze microstructure. This analysis was used to explain the occurrence of different failure modes (fast fracture, peeling, and base metal failure) and to make suggestions for improved methods for conducting and analyzing brazed SLJ tensile tests. The newer BFM is shown to provide significantly better corrosion resistance for a moderate reduction in mechanical strength.

     

Multiscale Elasticity of Tissue Engineering Scaffolds with Tissue-Engineered Bone: A Continuum Micromechanics Approach

Tissue engineering (TE) is the use of a combination of biological cells, engineering and materials methods, and of suitable biochemical and physicochemical factors, in order to improve or replace biological functions. It has brought the advent of entirely new classes of hierarchically organized, multiporous materials, consisting of both chemically and biologically produced parts. Here, we aim at contributing to the unsettled question of the mechanical functioning of bone tissue-engineering scaffolds with tissue-engineered bone—from a theoretical and applied mechanics viewpoint. Therefore, we build on recently developed microelasticity models for vertebrate bone and hydroxyapatite biomaterials, respectively. Tissue engineering scaffolds with tissue-engineered bone are micromechanically represented as tissue-engineered bone-coated macropores in a matrix built up by microporous hydroxyapatite polycrystals, based on an extension toward anisotropy, of Herve–Zaoui’s n-layered inclusion problem. The stiffness of macroporous hydroxyapatite-based TE scaffolds with newly ingrown bone is mainly governed by their porosities [vascular (macro) porosity defined through initial scaffold design and volume fraction of ingrown bone; and intercrystalline (micro) porosity between the hydroxyapatite crystals of the scaffold matrix material], while being less influenced by the type of bone growing inside the macropores. For a given degeneration kinetics of the scaffold, the microelastic models suggest apposition rates of bone needed to maintain the stiffness characteristics of the overall biomaterial-bone construct. This can be seen as a first step toward computer-aided engineering design of tissue-engineering scaffolds for large bone defect regeneration.     

Review of Dreams: A Key to Self-Knowledge.

In this book, readers are presented with another approach to decoding dreams--the Perceptanalytic Dream Interpretation System. Readers are told that the usual psychoanalytic mode of dream interpretation is flawed. Freud focused on the wish-fulfilling function of the dreams, but Piotrowski and Biele conceptualize dreams as unconscious attempts to clarify the dreamer's "personal intrapsychic conflicts" and to find solutions to the conflicts. They provide detailed "rules" and "axioms" to guide dream interpretation. However, Piotrowski and Biele do not offer any empirical evidence as to the reliability or validity of their dream interpretation rules. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rare earth containing catalysts for selective catalytic reduction of NO_x with ammonia:A Review

Increasingly stringent regulations in many countries require effective reduction and control of NOx emissions. To meet these limits, various methods have been exploited, among which the selective catalytic reduction of NOx using ammonia as the reductant(NH3-SCR) is the most favored technology. High catalytic activity, N2 selectivity and resistance to deactivation by sulfur, alkaline metals and hydrothermal conditions are the optimal properties of a successful SCR catalyst. Rare earth oxides, particularly CeO2, have been increasingly used to improve the catalytic activity and resistance to deactivation of deNOx catalysts, both modifying traditional vanadium catalysts, and also developing novel catalysts, especially for low temperature applications. This review summarized the open literature concerning recent research and development progresses in the application of rare earths for NH3-SCR of NOx. Additionally, the roles of rare earths in enhancing the performance of NH3-SCR catalyst were reviewed.     

The Constant-Stress,Constant-Heating-Rate Test: A Novel Method for Characterizing Transient Mechanical Behavior of Metallic Materials

Metallurgical and Materials Transactions A - A novel mechanical test for characterizing the transient, on-heating mechanical behavior of metallic structural materials was developed. It comprises...     

Review of Bulimia: A guide to recovery.

Reviews the book, Bulimia: A guide to recovery by Lindsey Hall and Leigh Cohn (1986). This self-help book is presented in three parts. The opening section includes two chapters. The first consists of answers to common questions about bulimia such as: What is bulimia? Is it dangerous? Why do people become bulimic? Why are bulimics mainly women? What does it feel like to binge-vomit? The answers to these questions are accurate, informative, and concise. The second chapter is the personal story of Lindsey Hall's nine-year history of binging and purging. The second section of the book, entitled "Overcoming Bulimia" and addressed to individuals coping with bulimia, includes a systematic approach to dealing with the disorder. Logical, practical ways to undertake the self-change process are presented. The final section of the book contains a variety of appendices including a 2-week program to stop binging and a guide for developing a bulimia support group. This brief book is an excellent adjunct to therapy for bulimia. In describing her struggle to overcome a serious eating disorder, Lindsey Hall serves as an appropriate coping model for others dealing with bulimia. Her honest account of repeated efforts at self-change are instructive and inspirational. I suspect that many clients will be able to identify with her and her struggle to change and will be positively motivated by this book. I am less optimistic about the value of the book without some form of treatment by a professional or recognized self-help organization. As is often the case with self-help books, it is questionable whether clients can successfully apply the recommended treatment strategies on their own. Nonetheless, I found the book to be informative, interesting, and well written. I recommend it highly as an adjunct to treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Features of style classification: A multivariate experimental analysis of children's responses to drawings.

Investigated the sensitivity of 48 children (aged 6–11 yrs) to the formal or stylistic properties of line drawings. Particular emphasis was placed on a detailed analysis of Ss' classifications through the use of multidimensional scaling and multiple-regression analyses. Ss were asked to judge the similarity of 12 line drawings that were specially prepared to vary along 3 dimensions (thickness, amount of shading, and expressiveness), which were shown to be salient in 12 adults' discriminations. The scaling and regression analyses confirmed that the youngest Ss were able to make systematic stylistic comparisons utilizing the 3 dimensions of line variation contained in the drawings. The significance of this finding is discussed in relation to research on children's perception of multidimensional relations. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coming to terms with coming out: Review and recommendations for family systems-focused research.

For lesbian, gay, and bisexual (LGB) adolescents and young adults, coming out to family members, especially parents, is a major psychological decision and hurdle due to both perceived fears and actual negative consequences. But beyond the literature on factors associated with the decision to come out and parents' initial reactions to the disclosure, empirical studies of what unfolds afterward, and how the family adjusts to the LGB adolescent's identity over time, are sparse and scattered. This article reviews and integrates findings from studies of the individual-, dyadic-, and family-level variables associated with positive outcomes, focusing particularly on relationship variables. Methodological concerns within this body of research are discussed, and research recommendations are offered. A preliminary working model of how families successfully come to terms with coming out is proposed to guide future research that will advance theory and clinical work with LGB youth and their families. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermomechanical Processing of Metal Feedstock for Semisolid Forming: A Review

Metallurgical and Materials Transactions B - Thermomechanical processing of cast structures is an effective solid working route of generating thixotropic morphologies after subsequent partial...     

Features of Technology for Pipe Steel Modification with Calcium and Cerium with Specification for Resistance to H2S-MEDIA

Metallurgist - Among many factors influencing steel resistance to hydrogen induced cracking, the sulfur content in the metal and steel modification technology with calcium are of particular...