Additive manufacturing by selective electron beam melting is a promising way to fabricate complex Ti–6Al–4V components. Sound parts can be realized by applying quite different processing strategies, ...which have an influence not only on processing time but also on the microstructure and the alloy composition. In this work, the processing window for Ti–6Al–4V is determined for a wide range of scanning speeds and line energies. The influence of the energy input on the resulting heat-affected zone and alloy composition is discussed.
Summary
An analysis of United States (US) Medicare claims data from 2002 to 2015 for women aged ≥ 65 years found that age-adjusted hip fracture rates for 2013, 2014, and 2015 were higher than ...projected, resulting in an estimated increase of more than 11,000 hip fractures.
Introduction
Hip fractures are a major public health concern due to high morbidity, mortality, and healthcare expenses. Previous studies have reported a decrease in the annual incidence of hip fractures in the US beginning in 1995, coincident with the introduction of modern diagnostic tools and therapeutic agents for osteoporosis. In recent years, there has been less bone density testing and fewer prescriptions for osteoporosis treatments. The large osteoporosis treatment gap raises concern of possible adverse effects on hip fracture rates.
Methods
We assessed hip fracture incidence in the US to determine if the previous decline in hip fracture incidence continued. Using 2002 to 2015 Medicare Part A and Part B claims for women ≥ 65 years old, we calculated age-adjusted hip fracture rates, weighting to the 2014 population.
Results
We found that hip fracture rates declined each year from 2002 to 2012 and then plateaued at levels higher than projected for years 2013, 2014, and 2015.
Conclusions
The plateau in age-adjusted hip fracture incidence rate resulted in more than 11,000 additional estimated hip fractures over the time periods 2013, 2014, and 2015. We recommend further study to assess all factors contributing to this remarkable change in hip fracture rate and to develop strategies to reduce the osteoporosis treatment gap.
► Creep strength of some Co-base alloys similar to Ni alloy IN100 at 850°C. ► Strengthening of grain boundaries is crucial for the creep strength. ► Morphology of grain boundaries has a strong impact ...on creep properties. ► Activation energy for creep similar to Ni-base superalloys. ► Plasticity by dislocation activity in matrix channels and shearing of γ′-particles.
The influence of various alloying elements on the creep properties of polycrystalline Co-base superalloys hardened by a ternary L12 compound, Co3(Al,W) (γ′-phase), was investigated. A Ti containing quaternary alloy shows creep strength similar to Ni-base superalloys IN100 and IN713C at 850°C and strongly superior to conventional Co-base superalloys as Haynes188. The activation energy for creep between 850 and 950°C is similar to the polycrystalline Ni-base superalloy IN100 in the same temperature range. Strengthening of the grain boundaries by third phase precipitates was found to be crucial for the mechanical properties. This can be achieved either by precipitation of borides or by additional intermetallic phases which precipitate due to oversaturation. During compressive creep at 850°C only a slight tendency for directional coarsening occurs, while at 950°C distinct γ/γ′-rafts perpendicular to the external compressive stress axis are formed which indicate a positive lattice misfit even at 950°C.
Selective electron beam melting (SEBM) is an additive manufacturing method where complex parts are built from metal powders in layers of typically 50µm. An electron beam is used for heating (about ...900°C building temperature) and selective melting of the material. The grain structure evolution is a result of the complex thermal and hydrodynamic conditions in the melt pool. We show how different scanning strategies can be used to produce either a columnar grain structure with a high texture in building direction or an equiaxed fine grained structure. Numerical simulations of the selective melting process are applied to study the fundamental mechanisms responsible for differing grain structures. It is shown, that the direction of the thermal gradient during solidification can be altered by scanning strategies to acquire either epitaxial growth or stray grains. We show that it is possible to locally alter the grain structure of a part, thus allowing tailoring of the mechanical properties.
Despite intense investigation, acute respiratory distress syndrome (ARDS) remains an enormous clinical problem for which no specific therapies currently exist. In this study, we used intratracheal ...lipopolysaccharide or Pseudomonas bacteria administration to model experimental acute lung injury (ALI) and to further understand mediators of the resolution phase of ARDS. Recent work demonstrates macrophages transition from a predominant proinflammatory M1 phenotype during acute inflammation to an anti-inflammatory M2 phenotype with ALI resolution. We tested the hypothesis that IL-4, a potent inducer of M2-specific protein expression, would accelerate ALI resolution and lung repair through reprogramming of endogenous inflammatory macrophages. In fact, IL-4 treatment was found to offer dramatic benefits following delayed administration to mice subjected to experimental ALI, including increased survival, accelerated resolution of lung injury, and improved lung function. Expression of the M2 proteins Arg1, FIZZ1, and Ym1 was increased in lung tissues following IL-4 treatment, and among macrophages, FIZZ1 was most prominently upregulated in the interstitial subpopulation. A similar trend was observed for the expression of macrophage mannose receptor (MMR) and Dectin-1 on the surface of alveolar macrophages following IL-4 administration. Macrophage depletion or STAT6 deficiency abrogated the therapeutic effect of IL-4. Collectively, these data demonstrate that IL-4-mediated therapeutic macrophage reprogramming can accelerate resolution and lung repair despite delayed use following experimental ALI. IL-4 or other therapies that target late-phase, proresolution pathways may hold promise for the treatment of human ARDS.
The optimization and manufacturing of an auxetic structure is presented. An inverse homogenization method is used to obtain the optimized geometry shown in the figure. The resulting structure is then ...produced using selective electron beam melting. The numerically predicted properties are experimentally verified.
The precipitation of topologically close packed (TCP) phases is detrimental for the high temperature strength of high refractory Ni-based superalloys. The beneficial influence of Ru with respect to ...this so called instability is nowadays well accepted. In the present paper the precipitation of topologically close packed (TCP) phases is studied quantitatively in two experimental alloys (one Ru-free and one with addition of Ru) to clarify the mechanism of the Ru effect. It is confirmed that the TCP phase precipitates undergo sequential phase transformation with the tetragonal σ-phase precipitating first. Ru retards the phase transformation and leads to decreased equilibrium volume fraction of TCP phases. The results clearly indicate that Ru decreases the driving force for TCP phase precipitation. Investigations of crystallography and chemistry of the TCP/matrix interface point to an additional effect by increase of misfit strain energy.
Improvements in phase stability on the addition of Ru are well known in the field of nickel-based superalloy development. However, the key mechanism of this benefit remains unclear. A new alloy ...series with stepwise increased additions of Ru was used to systematically investigate the impact of Ru on yopologically close-packed (TCP) phase inhibition. In addition, the investigation was carried out on a less known type of TCP formation, the so-called discontinuous precipitation. This type of TCP phase formation offers two major advantages compared with commonly investigated TCP plates in dendritic regions. First, the microstructure is much coarser than fine TCP plates, allowing reliable and less time consuming investigations. Second, discontinuous precipitation transforms the supersaturated and unstable γ/γ′ microstructure in a condition close to equilibrium, permitting a meaningful insight into the stable alloy constitution. The experimental results for alloy phase stability dependence on Ru are evaluated with respect to all possible effects of TCP phase inhibition by Ru. Furthermore, experimental evidence for increased Re solubility in the γ matrix was found on addition of Ru, which is not seen in corresponding ThermoCalc calculations. This finding is probably the dominant reason for the increased TCP phase capability of Ru-containing alloys. A ternary phase diagram model has been developed to describe the new approach.
A new mesoscale model was developed to understand the precipitation sequence of topologically close-packed (TCP) phases in single-crystal nickel-base superalloys. Nucleation and growth phenomena are ...described in detail. The model allows the multicomponent, multiphase and multiparticle calculation of TCP phase volume fractions and size distributions from supersaturated solid solution to thermodynamic equilibrium. It is based on the numerical Kampmann–Wagner method and applies CALPHAD (ThermoCalc) and DICTRA methodology for thermodynamics and diffusion. The capabilities of the simulations are demonstrated by the prediction of the size distributions of TCP phases and comparison with experimental data.
The influence of Re and Ru on phase diagram, as-cast microstructure, and segregation behavior has been investigated using a series of 12 experimental nickel-base superalloys derived from the parent ...alloy CSMX-4. Up to 2 at. pct Re and 4 at. pct Ru were added at the expense of nickel, while all other alloying elements were kept constant. The Re is found to increase the liquidus temperature and to decrease the
γ
′-solvus. The Re additions also strongly increase the amount of eutectic and the tendency for microsegregation. The Ru, on the other hand, displays much weaker effects or even no effect at all. The effects of Re on the eutectic formation and on segregation are shown to be related. Calculations based on ThermoCalc software were carried out and compared with the experimental results. ThermoCalc is found to be able to predict the changes in the phase diagram rather well. However, the calculation of the eutectic fraction with the Scheil–Gulliver model is not satisfying, which is due to the one-dimensionality of the model.
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