Manufacturing of high strength and high conductivity copper with laser powder bed fusion.

Additive manufacturing (AM), known as 3D printing, enables rapid fabrication of geometrically complex copper (Cu) components for electrical conduction and heat management applications. However, pure Cu or Cu alloys produced by 3D printing often suffer from either low strength or low conductivity at room and elevated temperatures. Here, we demonstrate a design strategy for 3D printing of high strength, high conductivity Cu by uniformly dispersing a minor portion of lanthanum hexaboride (LaB6) nanoparticles in pure Cu through laser powder bed fusion (L-PBF). We show that trace additions of LaB6 to pure Cu results in an improved L-PBF processability, an enhanced strength, an improved thermal stability, all whilst maintaining a high conductivity. The presented strategy could expand the applicability of 3D printed Cu components to more demanding conditions where high strength, high conductivity and thermal stability are required.

Training high-strength aluminum alloys to withstand fatigue.

The fatigue performance of high strength aluminum alloys used in planes, trains, trucks and automobiles is notoriously poor. Engineers must design around this important limitation to use Al alloys for light-weighting of transportation structures. An alternative concept for microstructure design for improved fatigue strength is demonstrated in this work. Microstructures are designed to exploit the mechanical energy imparted during the initial cycles of fatigue to dynamically heal the inherent weak points in the microstructure. The fatigue life of the highest strength Aluminum alloys is improved by 25x, and the fatigue strength is raised to ~1/2 the tensile strength. The approach embraces the difference between static and dynamic loading and represents a conceptual change in microstructural design for fatigue.

Case 275: Multiple Hepatic Hydatid Cysts.

HistoryA 61-year-old woman presented to the cardiology service with sinus tachycardia. As part of her work-up, she underwent routine echocardiography that showed a normal heart but incidentally revealed multiple lesions in the liver. An outpatient CT scan was performed to characterize the liver lesions. The patient had emigrated to Canada from the Middle East several years earlier and had no medical history of note; in particular, there was no history of cancer or predisposing factors for chronic liver disease. The patient's clinical examination findings; laboratory test results, including complete blood count; and liver function test results were normal.

Case 275.

HistoryA 61-year-old woman presented to the cardiology service with sinus tachycardia. As part of her work-up, she underwent routine echocardiography that showed a normal heart but incidentally revealed multiple lesions in the liver (Fig 1). An outpatient CT scan was performed to characterize the liver lesions (Figs 2-5). The patient had emigrated to Canada from the Middle East several years earlier and had no medical history of note; in particular, there was no history of cancer or predisposing factors for chronic liver disease. The patient's clinical examination findings; laboratory test results, including complete blood count; and liver function test results were normal.[Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text].

Precipitation strengthening of aluminum alloys by room-temperature cyclic plasticity.

High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature "bakes" (120° to 200°C) to form a high number density of nanoparticles by solid-state precipitation. We found that a controlled, room-temperature cyclic deformation is sufficient to continuously inject vacancies into the material and to mediate the dynamic precipitation of a very fine (1- to 2-nanometer) distribution of solute clusters. This results in better material strength and elongation properties relative to traditional thermal treatments, despite a much shorter processing time. The microstructures formed are much more uniform than those characteristic of traditional thermal treatments and do not exhibit precipitate-free zones. These alloys are therefore likely to be more resistant to damage.

Additive manufacturing of metals: a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys.

We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process-microstructure-property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts.

Bilateral Posterior Native Hip Dislocations after Fall from Standing.

We present a case of bilateral posterior native hip dislocations after a fall from standing. This exceedingly rare diagnosis is classically associated with younger patients whose bones are strong enough to dislocate rather than fracture in the setting of a high-momentum collision. We present an unusual case of an 88-year-old male with native hips who sustained a low-energy collision after falling from standing and was found to have bilateral posterior hip dislocations without associated pelvis or femur fractures.

Corrosion-wear of ß-Ti alloy TMZF (Ti-12Mo-6Zr-2Fe) in simulated body fluid.

UNLABELLED: Titanium alloys are popular metallic implant materials for use in total hip replacements. Although, α+ß titanium alloys such as Ti-6Al-4V have been the most commonly used alloys, the high Young's modulus (∼110GPa) leads to an undesirable stress shielding effect. An alternative is to use ß titanium alloys that exhibit a significantly lower Young's modulus (∼70GPa). Femoral stems made of a ß titanium alloy known as TMZF (Ti-12Mo-6Zr-2Fe (wt.%)) have been used as part of modular hip replacements since the early 2000's but these were recalled in 2011 by the US Food & Drug Administration (FDA) due to unacceptable levels of 'wear debris'. The wear was caused by small relative movement of the stem and neck at the junction where they fit together in the modular hip replacement design. In this study, the corrosion and wear properties of the TMZF alloy were investigated in simulated body fluid to identify the reason for the wear debris generation. Ti64 was used as a control for comparison. It is shown that the interaction between the surfaces of Ti64 and TMZF with simulated body fluid is very similar, both from the point of view of the products formed and the kinetics of the reaction. The dry wear behaviour of TMZF is also close to that of Ti64 and consistent with expectations based on Archard's law for abrasive wear. However, wear of Ti64 and TMZF in simulated body fluid show contrasting behaviours. A type of time-dependent wear test is used to examine the synergy between corrosion and wear of TMZF and Ti64. It is shown that the wear of TMZF accelerated rapidly in SBF whereas that of Ti64 is reduced. The critical role of the strain hardening capacity of the two materials and its role in helping the surface resist abrasion by hydroxyapatite particles formed as a result of the reaction with the SBF is discussed and recommendations are made for modifications that could be made to the TMZF alloy to improve the corrosion-wear response. STATEMENT OF SIGNIFICANCE: TMZF is a low modulus ß-Ti alloy that has been used as the femoral stem in the Stryker modular design total hip replacement. It went into service in the early 2000's but was recalled by the FDA in 2011 due to unacceptable levels of wear debris released in the body which led to adverse physiological reactions. A large number of these implants remain in patients today. In this contribution, we investigate the corrosion (interaction of the alloy with simulated body fluid (SBF)), dry wear and then corrosion-wear in SBF to identify the origin of the unacceptable levels of wear that led to the FDA recall of this material. We use Ti-6Al-4V as a control and demonstrate that the reaction between Ti64 and TMZF with SBF is very similar in terms of both products formed and kinetics. We also show that the dry wear behaviour of TMZF is very similar to that of Ti64 and exactly as should be expected for the hardness of this material. However, the wear behaviours of TMZF and Ti64 are completed different in SBF and wear of TMZF is significantly accelerated in SBF. A type of time-dependent wear test is used to demonstrate the synergy between corrosion and wear and the key role of the strain hardening capacity (or lack thereof in the case of ß-Ti) is discussed.