The fracture and fatigue properties of a newly developed bulk metallic glass alloy, Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (at. pct), have been examined. Experimental measurements using conventional fatigue precracked compact-tension C(T) specimens (ϳ7-mm thick) indicated that the fully amorphous alloy has a plane-strain fracture toughness comparable to polycrystalline aluminum alloys. However, significant variability was observed and possible sources are identified. The fracture surfaces exhibited a vein morphology typical of metallic glasses, and, in some cases, evidence for local melting was observed. Attempts were made to rationalize the fracture toughness in terms of a previously developed micromechanical model based on the Taylor instability, as well as on the observation of extensive crack branching and deflection. Upon partial or complete crystallization, however, the alloy was severely embrittled, with toughnesses dropping to ϳ1 MPaΊm. Commensurate with this drop in toughness was a marginal increase in hardness and a reduction in ductility (as measured via depthsensing indentation experiments). Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline steel and aluminum alloys. Moreover, the crack-advance mechanism was associated with alternating blunting and resharpening of the crack tip. This was evidenced by striations on fatigue fracture surfaces. Conversely, the (unnotched) stress/life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily, due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a low fatigue limit of ϳ4 pct of ultimate tensile strength.

The recent development of metallic alloy systems which can be processed with an amorphous structure over large dimensions, specifically to form metallic glasses at low cooling rates ͑ϳ10 K/s͒, has permitted novel measurements of important mechanical properties. These include, for example, fatigue-crack growth and fracture toughness behavior, representing the conditions governing the subcritical and critical propagation of cracks in these structures. In the present study, bulk plates of a Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 alloy, machined into 7 mm wide, 38 mm thick compact-tension specimens and fatigue precracked following standard procedures, revealed fracture toughnesses in the fully amorphous structure of K Ic ϳ55 MPaͱm, i.e., comparable with that of a high-strength steel or aluminum alloy. However, partial and full crystallization, e.g., following thermal exposure at 633 K or more, was found to result in a drastic reduction in fracture toughness to ϳ1 MPaͱm, i.e., comparable with silica glass. The fully amorphous alloy was also found to be susceptible to fatigue-crack growth under cyclic loading, with growth-rate properties comparable to that of ductile crystalline metallic alloys, such as high-strength steels or aluminum alloys; no such fatigue was seen in the partially or fully crystallized alloys which behaved like very brittle ceramics. Possible micromechanical mechanisms for such behavior are discussed. © 1997 American Institute of Physics. ͓S0003-6951͑97͒03730-3͔The recent development of alloys for the processing of metallic glasses in bulk form 1 permits the measurement of important mechanical properties in amorphous metals, in particular the fatigue and fracture characteristics. Previous work on metallic glasses has invariably been confined to very thin ribbons or wires, thus making measurements difficult.2,3 Few results are thus available on the toughness and cyclic crack growth properties in these alloys. Accordingly, the objective of the current study is to quantify the fracture toughness and fatigue-crack growth properties of a recently developed bulk metallic glass alloy, Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ͑nominal composition in at. %͒. [4][5][6] In this note, we present results characterizing the hardness, fracture toughness, and fatigue resistance of this alloy; in addition, we compare properties in the fully amorphous structure with that of partially and fully crystallized structures in the same alloy.As-received plates of the alloy, processed using methods described elsewhere, 1 were found to be fully amorphous. By heat treating at 633 K for 12 h in vacuo, just above the glass-transition temperature ͑T g ϳ625 K͒, a partially crystallized structure was formed. This consists of the amorphous matrix containing finely dispersed 3-5 nm nanocrystallites of a Cu-rich, Ti-rich fcc phase with an average spacing of ϳ20 nm between nanocrystals. 4,5 The volume fraction of the crystalline fcc phase is estimated from x ray and TEM data to be less than 5% of the sample. By heat treating at 723 K f...

“In situ toughened” silicon carbides, containing Al, B, and C additives, were prepared by hot pressing. Densification, phase transformations, and microstructural development were described. The microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD. The modulus of rupture was determined from fourpoint bend tests, while the fracture toughness was derived either from bend tests of beam‐shaped samples with a controlled surface flaw, or from standard disk‐shaped compact‐tension specimens precracked in cyclic fatigue. The R‐curve behavior of an in situ toughened SiC was also examined. A steady‐state toughness over 9 MPa·m1/2 was recorded for the silicon carbide prepared with minimal additives under optimum processing conditions. This increase in fracture toughness, more than a factor of three compared to that of a commercial SiC, was achieved while maintaining a bend strength of 650 MPa. The mechanical properties were found to be related to a microstructure in which platelike grain development had been promoted and where crack bridging by intact grains was a principal source of toughening.

Pores for thought: Chemical liquid deposition of silica onto ZSM-5 catalysts led to smaller pore openings that resulted in >90% selectivity for p-xylene over the other xylenes in the catalytic fast pyrolysis of furan and 2-methylfuran (see scheme). The p-xylene selectivity increased from 51% with gallium spray-dried ZSM-5 to 72% with a pore-mouth-modified catalyst in the pyrolysis of pine wood.

Weniger ist mehr: Die nasschemische Ablagerung von Kieselsäure auf ZSM‐5‐Katalysatoren führt zu verengten Porenöffnungen, was wiederum die Selektivität für p‐Xylol gegenüber den anderen Xylolen in der schnellen katalytischen Pyrolyse von Furan und 2‐Methylfuran auf über 90 % erhöht (siehe Schema). Die p‐Xylol‐Selektivität in der Pyrolyse von Kiefernholz steigt von 51 % mit sprühgetrocknetem Gallium‐ZSM‐5 auf 72 % mit einem Katalysator mit modifizierter Porenöffnung.

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BackgroundPotassium ethylenediaminetetraacetic acid (EDTA) is a sample tube anticoagulant used for many laboratory analyses. Gross potassium EDTA contamination of blood samples is easily recognised by marked hyperkalaemia and hypocalcaemia (1-3). Subtle potassium EDTA contamination, however, is a relatively common often unrecognised erroneous cause of spurious hyperkalaemia (2). This has the potential to adversely affect patient care and waste healthcare resources (4,5).In addition to hyperkalaemia and hypocalcaemia, potassium EDTA contamination may also cause hypomagnesaemia (1,2) and hypozincaemia (2). There are, however, no data on the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia. We therefore audited the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia over a 1-month period. MethodsFollowing a recent service evaluation (2), we routinely measure EDTA in serum samples from patients with unexplained hyperkalaemia (serum potassium > 6.0 mmol ⁄ l).In addition, over a 1-month period EDTA concentrations were measured in hypocalcaemic (serum adjusted calcium < 2.0 mmol ⁄ l), hypomagnesaemic (serum magnesium < 0.7 mmol ⁄ l) and hypozincaemic (serum zinc < 11 lmol ⁄ l) serum samples.Blood samples for routine serum biochemistry, plasma glucose and routine haematology are respectively collected into Sarstedt serum ⁄ z4 gel tubes, S U M M A R YBackground: Potassium ethylenediaminetetraacetic acid (EDTA) is a sample tube anticoagulant used for many laboratory analyses. Gross potassium EDTA contamination of blood samples is easily recognised by marked hyperkalaemia and hypocalcaemia. However, subtle contamination is a relatively common, often unrecognised erroneous cause of spurious hyperkalaemia. Potassium EDTA contamination may also cause hypomagnesaemia and hypozincaemia. There are, however, no data on the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia. Methods: Following a recent service evaluation, we measure EDTA in serum samples from patients with unexplained hyperkalaemia (serum potassium > 6.0 mmol ⁄ l). In addition, over a 1-month period EDTA concentrations were measured in hypocalcaemic (serum adjusted calcium < 2.0 mmol ⁄ l), hypomagnesaemic (serum magnesium < 0.7 mmol ⁄ l) and hypozincaemic (serum zinc < 11 lmol ⁄ l) serum samples. Results: Ethylenediaminetetraacetic acid contamination was detected in 31 samples, nine of which were detected by our routine screening programme. The remaining 22 samples represented 14.3% (19 ⁄ 133) of hypocalcaemic samples, 4.8% (5 ⁄ 104) of hypomagnesaemic samples and 1.4% (2 ⁄ 139) of hypozincaemic samples. A total of 25 ⁄ 31 (80.6%) of patients were re-bled, of which 23 ⁄ 25 (92%) results normalised. Conclusions: Factitious hyperkalaemia, hypocalcaemia and hypomagnesaemia caused by potassium EDTA contamination in our studies are relatively common, and if unrecognised may adversely affect patient care and waste scarce healthcare reso...