Understanding fracture in laser additive manufactured bulk metallic glass through small-scale mechanical measurement

Bulk metallic glasses (BMGs) are amorphous metal alloys formed by fast cooling that display high strength and toughness with good resistance to corrosion and wear. One traditional limitation has been that BMG castings are often limited to \u3c1 cm dimensions due to the high cooling rates needed. The recent development of selective laser melting (SLM) of metallic glasses opens up the possibility of creating large BMG components with complex geometries. However, we have recently shown that additive manufactured BMGs exhibit poor ductility and toughness when compared to their traditionally as-cast (AC) counterparts (Fig. 1 A-C). Our work investigates how the processing route influences the structure of a Zr-based BMG, and how this is linked to mechanical performance. Evaluation at the micro-scale is critical, as thermal influences on the microstructure from laser-processing and melt-pool solidification exist at these length-scales. Experimental calorimetry results have shown enthalpic relaxation variation between cast Zr-based glasses and those manufactured with SLM-processing, suggesting differences in free volume for different processing routes. The effect on the fracture properties was studied using single edge notched beam bending tests: SLM-processed alloy showed significantly lower fracture toughness when compared with the as-cast alloy, and this was explained by energetic barriers for activating shear transformations in the glass, elucidated in detail using micro-pillar compression testing (Fig. 1 D/E). These results are further related to the glassy laser-processed structure through advanced structural analyses using synchrotron X-ray diffraction and nanoindentation. Please click Additional Files below to see the full abstract

Mechanical properties of suture materials in general and cutaneous surgery

Comprehensive studies comparing tensile properties of sutures are over 25 years old and do not include recent advances in suture materials. Accordingly, the objective of this paper is to investigate the tensile properties of commonly-used sutures in cutaneous surgery. Thirteen 3-0 sized modern sutures (four non-absorbable and nine absorbable) were tensile tested in both straight and knotted configurations according to the procedures outlined by the United States Pharmacopeia. Glycomer 631 was found to have the highest failure load (56.1 N) of unknotted absorbable sutures, while polyglyconate (34.2 N) and glycomer 631 (34.3 N) had the highest failure loads of knotted absorbable sutures. Nylon (30.9 N) and polypropylene (18.9 N) had the greatest failure loads of straight and knotted non-absorbable sutures, respectively. Polydioxane was found to have the most elongation prior to breakage (144%) of absorbable sutures. Silk (8701 MPa) and rapid polyglactin 910 (9320 MPa) had the highest initial modulus of nonabsorbable and absorbable sutures, respectively. The new data presented in the study provides important information for guiding the selection of suture materials for specific surgeries.Keywords: modulus, sutures, strength, elongation, tensile propertie

A highly efficient degradation mechanism of methyl orange using Fe-based metallic glass powders

A new Fe-based metallic glass with composition Fe₇₆B₁₂Si₉Y₃ (at. %) is found to have extraordinary degradation efficiency towards methyl orange (MO, C₁₄H₁4N₃SO₃) in strong acidic and near neutral environments compared to crystalline zero-valent iron (ZVI) powders and other Fe-based metallic glasses. The influence of temperature (294–328 K) on the degradation reaction rate was measured using ball-milled metallic glass powders revealing a low thermal activation energy barrier of 22.6 kJ/mol. The excellent properties are mainly attributed to the heterogeneous structure consisting of local Fe-rich and Fe-poor atomic clusters, rather than the large specific surface and strong residual stress in the powders. The metallic glass powders can sustain almost unchanged degradation efficiency after 13 cycles at room temperature, while a drop in degradation efficiency with further cycles is attributed to visible surface oxidation. Triple quadrupole mass spectrometry analysis conducted during the reaction was used to elucidate the underlying degradation mechanism. The present findings may provide a new, highly efficient and low cost commercial method for azo dye wastewater treatment.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Nature Publishing Group. The published article can be found at: http://www.nature.com/articles/srep2194

Ni-Nb-P-based bulk glass-forming alloys: Superior material properties combined in one alloy family

Ni-Nb-based bulk glass-forming alloys are among the most promising amorphous metals for industrial applications due to their incomparable combination of strength, hardness, elasticity and plasticity. However, the main drawback is the limited glass-forming ability, narrowing the field of application to solely small components. In this study, we show that minor additions of P to the binary Ni-Nb system increase the glass-forming ability by 150 % to a record value of 5 mm. P can be easily added by using an industrial Ni-P pre-alloy which is readily available. The partial substitution of Nb by Ta further boosts the glass-forming ability to values 200 % higher than that of the binary base alloy. Besides conventional X-ray diffraction measurements, the amorphous nature of the samples is verified by high-energy synchrotron X-ray diffraction experiments. Moreover, the mechanical properties of the new alloy compositions are characterized in uniaxial compression tests and Vickers hardness measurements, showing a high engineering yield strength of 3 GPa, an extended plastic regime up to 10 % strain to failure and an increase of the hardness to a maximum value of 1000 HV5. Additionally, calorimetric measurements reveal that the modified alloys feature an extended supercooled liquid region up to 69 K upon heating, permitting thermoplastic micro molding of amorphous feedstock material

A Highly Fatigue-Resistant Zr-Based Bulk Metallic Glass

The strength-normalized fatigue endurance strength of the bulk metallic glass (BMG) Zr₅₂.₅Cu₁₇.₉Ni₁₄.₆Al₁₀Ti₅ (Vitreloy 105) has been reported to be the highest for any BMG; however, to date, there has been no explanation of why this material is so much better than other Zr-based compositions. In this study, the fatigue-crack growth behavior of Zr₅₂.₅Cu₁₇.₉Ni₁₄.₆Al₁₀Ti₅ was compared in ambient air vs dry nitrogen environment. The excellent fatigue life behavior is attributed to a relatively high fatigue threshold (Kₜₕ ≈ 2 MPa√m) and a lack of sensitivity to environmental effects on fatigue-crack growth in ambient air, as compared to other Zr-based BMGs. Fatigue life experiments conducted in ambient air confirmed the excellent fatigue life properties with a 10⁷-cycle endurance strength of ~0.24 of the ultimate tensile strength; however, it was also found that casting porosity, even in limited amounts, could reduce this endurance strength by as much as ~60 pct. Overall, the BMG Zr₅₂.₅Cu₁₇.₉Ni₁₄.₆Al₁₀Ti₅ appears to have excellent strength and fatigue properties and should be considered as a prime candidate material for future applications where good mechanical fatigue resistance is required

Improving Participation of Engineering Students Studying Abroad: An International Dual Degree Program in Materials Science and Mechanical Engineering

Without AbstractThis is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Springer and can be found at: http://link.springer.com/journal/11837

Mo-Si-B Alloy Development

Mo-Si-B silicides consisting of the phases α-Mo (Mo solid solution), Mo3Si, and Mo5SiB2 have melting points on the order of 2000°C and have potential as ultra-high temperature structural materials. Mo-Si-B alloys can be processed such that the α-Mo is present in the form of isolated particles in a silicide matrix, or as a continuous matrix “cementing” individual silicide particles together. The latter microstructure is similar to that of WC-Co hard metals. This paper focuses on the relationship between the topology as well as scale of the microstructure of Mo-Mo3Si-Mo5SiB2 alloys, and their creep strength and fracture toughness. For example, the creep strength of Mo-Si-B alloys is improved by reducing the α-Mo volume fraction and by making the α-Mo phase discontinuous. The fracture toughness is improved by increasing the α-Mo volume fraction and by making the α-Mo phase continuous. Room temperature stress intensity factors as high as 21 MPa m 1/2 were obtained. The room temperature fracture toughness of Mo-Si-B alloys can also be improved by microalloying with Zr. The room temperature ductility of Mo itself can be improved by adding MgAl2O4 spinel particles suggesting yet another way to improve the ductile phase toughening of Mo-Si-B alloys

High temperature indentation based property measurements of IN-617

Inconel 617 (IN-617) mainly contains nickel (Ni), chromium (Cr), cobalt (Co) and molybdenum (Mo). IN-617 is widely used in applications that require high temperature operation due to its high temperature stability and strength as well as its strong resistance to oxidation and carburization. The current work focuses on the measurement of temperature dependent mechanical properties of IN-617 from room temperature (around 25 °C) up to 800 °C. The properties measured are reduced modulus, elastic modulus, hardness, indentation creep rate, indentation creep exponent, and thermal activation volume. The indentation size effect is analyzed as a function of temperature. Using a combination of optical microscopy and scanning electron microscopy (SEM) imaging, the effect of precipitate distribution and oxidation on the measured properties is found to be negligible beyond a critical indentation depth. The mean hardness value ranged from 3.1 GPa at room temperature to 1.6 GPa at 800 °C. A relation between indentation depth and hardness as a function of temperature change was used to extract strain gradient plasticity associated length scales with values changing from 1.0 μm at room temperature to 1.8 μm at 400 °C and to 1.6 μm at 800 °C