Effect of lamellar orientation and width on the strength and operating deformation mechanisms of fully lamellar TiAl alloys determined by micropillar compression

Titanium aluminide alloys are of interest for the aerospace industry due to their low density(3.9-4.2g/cm3), good high-temperature strength retention, high modulus and creep strength, as well as high resistance to oxidation. The TiAl alloys of commercial interest typically contain two phases: γ TiAl and a2 Ti3Al, but their microstructure can substantially vary depending on composition and thermomechanical history. They can be classified as fully lamellar, near lamellar, duplex or near gamma. Fully lamellar microstructures formed by colonies of lamellar γ and a2 phases are typically obtained after heat treatment at temperatures above the a-transus, with the soaking temperature and cooling rate [1] being critical variables to determine the microstructural parameters, such as colony size, volume fraction and lamellar width. They present the best high temperature strength [1-2]; However, they lack room temperature ductility, which has limited their application so far. In this context, several compositional families have been developed in the last years, especially as a function of alloying elements, such as, niobium, tantalum, tungsten or molybdenum, which stabilize the β phase affecting the volume fraction and size of lamellar colonies. Two of the most important families are TNB alloys, with high niobium concentration and small additions of boron and carbon, where solidification takes place through the phase and TNM alloys, with even larger additions of niobium and molybdenum. Solidification of TNM alloys takes place through the β phase inducing further grain refinement due to β→a transformation [3] during cooling. The lack of ductility of fully lamellar TiAl alloys is associated with the anisotropic deformation of individual colonies, as a function of lamellar orientation () with respect to the loading axis. In this regard, micropillar compression is a powerful technique to determine the different deformation modes of TiAl colonies as a function of lamellar orientation. This has been shown in previous studies for TNB alloys (Ti45Al2Nb2MnXB), where the outcomes of micropillar compression were compared with results obtained from macroscopic tests using polysynthetically twinned crystals (PTS) [4]. Three different deformation modes where found: a soft deformation mode (=45º) and two hard modes (=0º and =90º), due to the activation of different slip systems in each case. However, the role of lamellar width has not been studied in detail before. This work focuses on an alloy belonging to the TNM family, with the objective of studying the role of lamellar orientation and lamellar width on the anisotropic mechanical response of individual colonies. For this, a Ti43.5Al4Nb1MoXB alloy was subjected to different thermal treatments with the objective of refining the lamellar width. In particular, after heating up and soaking at 1260ºC (above the a-transus), three cooling rates were selected to cool down to 800ºC (a2 + β + γ region): 40ºC/min, 400ºC/min and 4000ºC/min. The cooling rate was reduced to 40ºC/min from 800ºC in all cases to avoid cracking. As a result, the average lamellar width was varied within a range of two orders of magnitude (from a few nanometers to more than 200nm) for the same alloy composition. The anisotropy of individual colonies and their deformation modes as a function of lamellar orientation were studied by micropillar compression. For this, square micropillars were milled by means of FIB with dimensions of 5 x 5 x 15m3. Uniaxial compression was carried out using a flat-punch diamond tip with a diameter of 10m under displacement control mode at a strain rate of 10-3 s-1 up to a maximum engineering strain of 10%. Deformed micropillars were analyzed to relate the orientation of lamellar interfaces with the activation of different deformation modes. The results are compared with those obtained in TNB alloys as well as a function of the average lamellar width. [1] F. Appel, J. Paul, M. Oehring, Gamma Titanium Aluminide Alloys: Science and Technology. Wiley, 2011. [2] M.E. Kassner, M.T. Pérez-Prado. Fundamentals of Creep in Metals and Alloys, Elsevier, 2004. [3] H. Clemens, S. Mayer, Adv. Eng. Mater. 15 (2013) 191–215. [4] A.J. Palomares-García, M.T. Pérez Prado, J.M. Molina-Aldareguia Acta Mater. 123 (2017) 102-114

Measuring the critical resolved shear stresses in Mg alloys by instrumented nanoindentation

One of the main limiting factors in the development of new magnesium (Mg) alloys with enhanced mechanical behavior is the need to use vast experimental campaigns for microstructure and property screening. For example, the influence of new alloying additions on the critical resolved shear stresses (CRSSs) is currently evaluated by a combination of macroscopic single-crystal experiments and crystal plasticity finite-element simulations (CPFEM). This time-consuming process could be considerably simplified by the introduction of high-throughput techniques for efficient property testing. The aim of this paper is to propose a new and fast, methodology for the estimation of the CRSSs of hexagonal close-packed metals which, moreover, requires small amounts of material. The proposed method, which combines instrumented nanoindentation and CPFEM modeling, determines CRSS values by comparison of the variation of hardness (H) for different grain orientations with the outcome of CPFEM. This novel approach has been validated in a rolled and annealed pure Mg sheet, whose H variation with grain orientation has been successfully predicted using a set of CRSSs taken from recent crystal plasticity simulations of single-crystal experiments. Moreover, the proposed methodology has been utilized to infer the effect of the alloying elements of an MN11 (Mg–1% Mn–1% Nd) alloy. The results support the hypothesis that selected rare earth intermetallic precipitates help to bring the CRSS values of basal and non-basal slip systems closer together, thus contributing to the reduced plastic anisotropy observed in these alloy

Prevalence of Symptomatic Axial Osteoarthritis Phenotypes in Spain and Associated Socio-Demographic, Anthropometric, and Lifestyle Variables

Epidemiology of RMDFinanciado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] Objective. Axial osteoarthritis (OA) is a common cause of back and neck pain, however, few studies have examined its prevalence. The aim was to estimate the prevalence and the characteristics of symptomatic axial OA in Spain. Methods. EPISER2016 is a cross-sectional multicenter population-based study of people aged 40 years or older. Subjects were randomly selected using multistage stratified cluster sampling. Participants were contacted by telephone to complete rheumatic disease screening questionnaires. Two phenotypes were analyzed, patients with Non-exclusive axial OA (NEA-OA) and Exclusive axial OA (EA-OA). To calculate the prevalence and its 95% confidence interval (CI), the sample design was considered and weighting was calculated according to age, sex and geographic origin. Results. Prevalence of NEA-OA by clinical or clinical-radiographic criteria was 19.17% (95% CI: 17.82–20.59). The frequency of NEA-OA increased with age (being 3.6 times more likely in patients aged 80 s or more than in those between 40 and 49 years) and body mass index. It was significantly more frequent in women, as well as in the center of Spain. It was less frequent in those with a higher level of education. Lumbar OA was more frequent than cervical OA. This difference grew with increasing age and was not associated with gender. It was also greater in overweight and obese subjects. Conclusions. This is the first study on the prevalence of axial OA phenotypes in Europe describing the associated socio-demographic, anthropometric, and lifestyle variables.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. EPISER2016 was supported by Celgene, Gebro Pharma, Merck Sharp & Dohme in Spain, Pfizer, and Sanofi-Aventis, none of whom had any role in the study design, data collection, data analysis, interpretation, or writing of this manuscript. MS was financed via the Rio Hortega Contract—Health Research Fund (CM17/00101), the Sanitary Research Fund integrated in the National Plan of Scientific Program, Technological Development and Innovation 2013–2016 and funded by the ISCIII-Subdirectorate General Evaluation and Promotion of Research-European Regional Development Fund (ERDF) "A way of making Europe

Impacto de la variabilidad intrapaciente en la concentración sanguínea de anticalcineurínicos en los resultados del trasplante cardiaco

[Abstract] Introduction and objectives. Intrapatient blood level variability (IPV) of calcineurin inhibitors has been associated with poor outcomes in solid-organ transplant, but data for heart transplant are scarce. Our purpose was to ascertain the clinical impact of IPV in a multi-institutional cohort of heart transplant recipients. Methods. We retrospectively studied patients aged ≥ 18 years, with a first heart transplant performed between 2000 and 2014 and surviving ≥ 1 year. IPV was assessed by the coefficient of variation of trough levels from posttransplant months 4 to 12. A composite of rejection or mortality/graft loss or rejection and all-cause mortality/graft loss between years 1 to 5 posttransplant were analyzed by Cox regression analysis. Results. The study group consisted of 1581 recipients (median age, 56 years; women, 21%). Cyclosporine immediate-release tacrolimus and prolonged-release tacrolimus were used in 790, 527 and 264 patients, respectively. On multivariable analysis, coefficient of variation > 27.8% showed a nonsignificant trend to association with 5-year rejection-free survival (HR, 1.298; 95%CI, 0.993-1.695; P = .056) and with 5-year mortality (HR, 1.387; 95%CI, 0.979-1.963; P = .065). Association with rejection became significant on analysis of only those patients without rejection episodes during the first year posttransplant (HR, 1.609; 95%CI, 1.129-2.295; P = .011). The tacrolimus-based formulation had less IPV than cyclosporine and better results with less influence of IPV. Conclusions. IPV of calcineurin inhibitors is only marginally associated with mid-term outcomes after heart transplant, particularly with the tacrolimus-based immunosuppression, although it could play a role in the most stable recipients.[Resumen] Introducción y objetivos. El objetivo es estudiar el impacto clínico de la variabilidad intrapaciente (VIP) de la concentración sanguínea de los anticalcineurínicos en el trasplante cardiaco, pues la información actual es escasa. Métodos. Se analizó retrospectivamente a pacientes de edad ≥ 18 años con un trasplante cardiaco realizado entre 2000 y 2014 y con supervivencia ≥ 1 año. La VIP se valoró mediante el coeficiente de variación de concentraciones entre los meses 4 a 12 postrasplante. El compuesto de rechazo, mortalidad o pérdida del injerto y la mortalidad o pérdida del injerto 1-5 años tras el trasplante se analizaron mediante regresión de Cox. Resultados. Se estudió a 1.581 receptores (edad, 56 años; mujeres, 21%), tratados con ciclosporina (790 pacientes) o tacrolimus (791 pacientes). En el análisis multivariable, un coeficiente de variación > 27,8% tendió a asociarse con el compuesto de rechazo/mortalidad (HR = 1,298; IC95%, 0,993-1,695; p = 0,056) y con la mortalidad (HR = 1,387; IC95%, 0,979-1,963; p = 0,065) a los 5 años. La asociación con el rechazo fue significativa al analizar a la población sin rechazos durante el primer año del trasplante (HR = 1,609; IC95%, 1,129-2,295; p = 0,011). El tacrolimus tuvo menos VIP que la ciclosporina, junto con unos mejores resultados por la menor influencia de la VIP. Conclusiones. La VIP de los anticalcineurínicos, especialmente con la inmunosupresión basada en el tacrolimus, se asocia solo marginalmente con los resultados a medio plazo del trasplante cardiaco, aunque puede tener influencia en los pacientes más estables durante el primer año tras el trasplante

The Falling Incidence of Hematologic Cancer After Heart Transplantation

[Abstract] Background. A number of changes in the management of heart transplantation (HT) patients have each tended to reduce the risk of post-HT hematologic cancer, but little information is available concerning the overall effect on incidence in the HT population. Methods. Comparison of data from the Spanish Post-Heart-Transplantation Tumour Registry for the periods 1991–2000 and 2001–2010. Results. The incidence among patients who underwent HT in the latter period was about half that observed in the former, with a particularly marked improvement in regard to incidence more than five yr post-HT. Conclusions. Changes in HT patient management have jointly reduced the risk of hematologic cancer in the Spanish HT population. Long-term risk appears to have benefited more than short-term risk

Impacto de la edad del donante-receptor en la supervivencia al trasplante cardiaco. Subanálisis del Registro Español de Trasplante Cardiaco

[Abstract] Introduction and objectives. The age of heart transplant recipients and donors is progressively increasing. It is likely that not all donor-recipient age combinations have the same impact on mortality. The objective of this work was to compare survival in transplant recipients according to donor-recipient age combinations. Methods. We performed a retrospective analysis of transplants performed between 1 January 1993 and 31 December 2017 in the Spanish Heart Transplant Registry. Pediatric transplants, retransplants and combined transplants were excluded (6505 transplants included). Four groups were considered: a) donor < 50 years for recipient < 65 years; b) donor < 50 years for recipient ≥ 65 years; c) donor ≥ 50 years for recipient ≥ 65 years, and d) donor ≥ 50 years for recipient < 65 years. Results. The most frequent group was young donor for young recipient (73%). There were differences in the median survival between the groups (P < .001): a) younger-younger: 12.1 years, 95%CI, 11.5-12.6; b) younger-older: 9.1 years, 95%CI, 8.0-10.5; c) older-older: 7.5 years, 95%CI, 2.8-11.0; d) older-younger: 10.5 years, 95%CI, 9.6-12.1. On multivariate analysis, independent predictors of mortality were the age of the donor and the recipient (0.008 and 0.001, respectively). The worst combinations were older-older vs younger-younger (HR, 1.57; 95%CI, 1.22-2.01; P < .001) and younger-older vs younger-younger (HR, 1.33; 95%CI, 1.12-1.58; P = .001). Conclusions. Age (of the donor and recipient) is a relevant prognostic factor in heart transplant. The donor-recipient age combination has prognostic implications that should be identified when accepting an organ for transplant.[Resumen] Introducción y objetivos. La edad de receptores y donantes cardiacos se está incrementando progresivamente. Es probable que no todas las combinaciones tengan el mismo impacto en la mortalidad. El objetivo de este trabajo es comparar la supervivencia de los pacientes trasplantados según la combinación de edades de donante y receptor. Métodos. Análisis retrospectivo del Registro Español de Trasplante Cardiaco de los trasplantes realizados entre el 1 de enero de 1993 y el 31 de diciembre de 2017. Se excluyeron los pediátricos, los retrasplantes y los trasplantes combinados (se incluyeron 6.505 trasplantes). Se consideraron 4 grupos: a) donante menor de 50 años para receptor menor de 65 años; b) donante menor de 50 años para receptor de edad ≥ 65 años; c) donante de edad ≥ 50 años para receptor de 65 o más, y d) donante de edad ≥ 50 años para receptor menor de 65. Resultados. El grupo más frecuente fue el de donante joven para receptor joven (73%). Hubo diferencias en la mediana de supervivencia entre los grupos (p < 0,001): a) joven-joven: 12,1 años (IC95%, 11,5-12,6); b) joven-mayor: 9,1 años (IC95%, 8,0-10,5); c) mayor-mayor: 7,5 años (IC95%, 2,8-11,0), y d) mayor-joven: 10,5 años (IC95%, 9,6-12,1). En el análisis multivariante, las edades del donante y del receptor resultaron predictoras independientes de la mortalidad (0,008 y 0,001 respectivamente). Las peores combinaciones fueron mayor-mayor frente a joven-joven (HR = 1,57; IC95%, 1,22-2,01; p < 0,001) y joven-mayor frente a joven-joven (HR = 1,33; IC95%, 1,12-1,58; p = 0,001). Conclusiones. La edad (del donante y del receptor) es un factor pronóstico relevante en el trasplante cardiaco. La combinación de edades de donante y receptor posee implicaciones pronósticas que se debe conocer a la hora de aceptar un órgano para trasplante

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn+0.8 vol pct TiB₂

The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB₂ intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.The authors are grateful to Industria de Turbo Propulsores, S.A. for supplying the intermetallic blades. Funding from the Spanish Ministry of Science and Innovation through projects MAT2009-14547-C02-01 and MAT2009-14547-C02-02 is acknowledged. The Madrid Regional Government supported this project partially through the ESTRUMAT grant P2009/MAT-1585. C.J.B. acknowledges the support from Grant SAB2009-0045 from the Spanish Ministry of Education for his sabbatical stage in Madrid.Publicad

Malignancy following heart transplantation: differences in incidence and prognosis between sexes – a multicenter cohort study

[Abstract] Male patients are at increased risk for developing malignancy postheart transplantation (HT); however, real incidence and prognosis in both genders remain unknown. The aim of this study was to assess differences in incidence and mortality related to malignancy between genders in a large cohort of HT patients. Incidence and mortality rates were calculated for all tumors, skin cancers (SCs), lymphoma, and nonskin solid cancers (NSSCs) as well as survival since first diagnosis of neoplasia. 5865 patients (81.6% male) were included. Total incidence rates for all tumors, SCs, and NSSCs were lower in females [all tumors: 25.7 vs. 44.8 per 1000 person‐years; rate ratio (RR) 0.68, (0.60–0.78), P < 0.001]. Mortality rates were also lower in females for all tumors [94.0 (77.3–114.3) vs. 129.6 (120.9–138.9) per 1000 person‐years; RR 0.76, (0.62–0.94), P = 0.01] and for NSSCs [125.0 (95.2–164.0) vs 234.7 (214.0–257.5) per 1000 person‐years; RR 0.60 (0.44–0.80), P = 0.001], albeit not for SCs or lymphoma. Female sex was associated with a better survival after diagnosis of malignancy [log‐rank p test = 0.0037; HR 0.74 (0.60–0.91), P = 0.004]. In conclusion, incidence of malignancies post‐HT is higher in males than in females, especially for SCs and NSSCs. Prognosis after cancer diagnosis is also worse in males

Effect of stress level on the high temperature deformation and fracture mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB²: an 'In Situ' experimental study

The effect of the applied stress on the deformation and crack nucleation and propagation mechanisms of a gamma-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) was examined by means of in situ tensile (constant strain rate) and tensile-creep (constant load) experiments performed at 973 K (700 °C) using a scanning electron microscope. Colony boundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa and during the tertiary stage of the creep tests performed at higher stresses. Colony boundary cracking was also observed in the constant strain rate tensile test. Interlamellar ledges were only found during the tensile-creep tests at high stresses (sigma > 400 MPa) and during the constant strain rate tensile test. Quantitative measurements of the nature of the crack propagation path along secondary cracks and along the primary crack indicated that colony boundaries were preferential sites for crack propagation under all the conditions investigated. The frequency of interlamellar cracking increased with stress, but this fracture mechanism was always of secondary importance. Translamellar cracking was only observed along the primary crack.Funding from the Spanish Ministry of Science and Innovation through projects (MAT2009-14547-C02-01 and MAT2009-14547-C02-02) is acknowledged. The Madrid Regional Government partially supported this project through the ESTRUMAT grant (P2009/MAT-1585). CJB acknowledges the support from the Spanish Ministry of Education for his sabbatical stay in Madrid (SAB2009-0045).Publicad