Growth Restriction Factors Research Articles

Study of phase evolution, mechanical, and tribological behaviour of a novel β-phase strengthened Ti-alloy with Fe and Co alloying via a laser material deposition route

A new Ti64-Fe-Co alloy was studied via a laser-material-deposition method. Associated with high growth restriction factors, β-eutectoid (Fe, Co) alloying minimizes anisotropy (due to the prior columnar β-grain growth) in the laseradditive -manufacturing (AM) built Ti-parts along with enhanced properties. Fe alloying for Ti64 via laser-AM results in superior strengthening with reduced ductility, where a good combination of strength and elongation properties can be achieved for a Ti-Fe-Co system. However, studies on Ti-Fe-Co-based systems via laser processing are limited. Co possesses a similar electronic property as Fe and the Ti-Fe system accompanies further solute addition. The effect of Co alloying the Ti64-Fe system was investigated in this study via a pre-placed laser-material-deposition method. A Ti64–5Fe-5Co alloy was formulated referring to CALPHAD simulations, along with a Ti64–10Fe composition. The new Ti-alloys were fabricated via both the laser-material-deposition and conventional vacuum arc melting routes, and the characteristics of the fabricated samples were examined. XRD analysis shows the evolution of the β-Ti phase with Fe and Co alloying, which agrees with the thermodynamic phase simulation results. The corresponding SEM micrographs depicted a β-phase dominant matrix with α-dendrites, and the solidification path was discussed. Considerable grain refinement was obtained for the laser-deposited alloys compared to the arc-melted ones, with an improved hardness value twice that of the commercial Ti64. A reduced stiffness for the laser-deposited Ti64–5Fe-5Co was observed from the load-vs-displacement characteristics, indicating matrix softening with Co alloying, which might benefit the elongation properties. The studied Ti-alloy shows a 30 % improvement in the dry-sliding wear characteristic with reduced fretting and abrasion compared to the commercial Ti64. The studied Ti-alloys were located in the theoretical d-electron space and new (Bo) ̅-(Md) ̅ vectors were introduced. Further studies on this would help in extending the applicability of laser-AM-built Ti-components.

Effect of manganese on grain morphology and microstructure of Ti-6Al-4V alloy by laser wire deposition

The addition of growth restricting elements in additive manufacturing of Ti and Ti-based alloys can result in the formation of equiaxed structures. However, an excessive incorporation of these elements frequently impairs the mechanical properties. Obtaining the minimum necessary amount of addition is crucial to achieve the transition from columnar to equiaxed microstructure. This ensures that the desired equiaxed structure is obtained while minimizing any potential negative effects on the material's properties. Here manganese was taken as the potential grain refiner in Ti alloy. Then, evolutions of grain morphologies and microstructures as well as the mechanical properties various of Ti-6Al-4V alloy in laser wire deposition additive manufacturing with the growth restriction factors of 26, 32, 39 were explored respectively. And the average hardness of the deposits were 495 HV, 512 HV, and 530 HV, respectively, showing an increase of approximately 15%, 19% and 23%. When the growth restricting factor value reached 39, the columnar prior β grains underwent a complete transformation into equiaxed grains. Mn elements promoted the decomposition of β→α+Mn2Ti during the multi-pass deposition and the microhardness of the deposits were significantly increased. Additionally, Mn elements were expelled outwards during the β→α transition. Nevertheless, the diffusion rate of Mn elements was low and thereby there was a low growth rate of α phases, thus refining α phases.

Underlying factors determining grain morphologies in high-strength titanium alloys processed by additive manufacturing

In recent research, additions of solute to Ti and some Ti-based alloys have been employed to produce equiaxed microstructures when processing these materials using additive manufacturing. The present study develops a computational scheme for guiding the selection of such alloying additions, and the minimum amounts required, to effect the columnar to equiaxed microstructural transition. We put forward two physical mechanisms that may produce this transition; the first and more commonly discussed is based on growth restriction factors, and the second on the increased freezing range effected by the alloying addition coupled with the imposed rapid cooling rates associated with AM techniques. We show in the research described here, involving a number of model binary as well as complex multi-component Ti alloys, and the use of two different AM approaches, that the latter mechanism is more reliable regarding prediction of the grain morphology resulting from given solute additions.

Development of an additively manufactured metastable beta titanium alloy with a fully equiaxed grain structure and ultrahigh yield strength

Metastable β titanium alloys usually suffer from relatively low yield strengths, which restricts their applications as a structural material. Additive manufacturing (AM), due to its extremely high cooling rates, can generate a refined microstructure that is beneficial to yield strength. However, the intrinsic steep thermal gradients within melt pools often lead to development of columnar grains that can result in mechanical anisotropy. To address these issues, we propose to use potent β-stabilizing elements with large growth restriction factors as the main solute elements in Ti, specifically Fe and Co. d-electron theory is also used to design the detailed compositions of the new titanium alloys for AM. A novel metastable titanium alloy, Ti-xFe-xCo-1Mo (1.5< x <3.5 at%), is thus developed by laser powder bed fusion (L-PBF). With process optimization, the L-PBF-processed alloy was found to contain fully equiaxed β grains embedded with α laths and ω precipitates and the grain boundaries decorated by Ti 2 Co precipitates. The matrix consists of a certain number of micro-sized β flecks and a high density of Fe and Mo atomic clusters. Upon solution treatment (ST), the microstructure turned into equiaxed β grains embedded with ultrafine ω precipitates and Mo atomic clusters. While the L-PBF-processed alloy shows poor tensile properties probably due to the presence of isothermal ω precipitates, the L-PBF-ST-processed alloy demonstrates an unprecedented yield strength of 1.2 GPa and a decent elongation of 10~12%. The alloy deformed by dislocation slipping and failed in a ductile fracture mode.

Grain refinement and abnormal peritectic solidification in WxNbTiZr high-entropy alloys

The microstructures of many high-entropy alloys (HEAs) can be understood or controlled based on traditional phase formation mechanisms. In this study, peritectic solidification was introduced to HEAs by designing novel WxNbTiZr peritectic high-entropy alloys (PHEAs). The phase constitutions and solidification microstructure evolutions of WxNbTiZr were clarified by combining experiments and thermodynamic simulations. Grain refinements were achieved in WxNbTiZr, which should attribute to the high growth restriction factors introduced by W solute and the segmentations of the primary phase during peritectic transformation. The significantly refined grains can simultaneously enhance the strength and ductility of the alloy. High fractions of peritectic phases and special pearl chain structures that are highly likely the products of peritectic solidification are seen in WxNbTiZr but not in the typical binary W-Zr peritectic alloy, highlighting that the compositional complexity featured by PHEAs could heavily influence peritectic reaction. The PHEAs idea is also generalized by developing WxMoTiZr alloys.

Associations of maternal hypertensive disorders during pregnancy with offspring risks of ischemic heart disease and stroke: a Nordic cohort study

Abstract Background A substantial body of evidence suggests that children exposed to maternal hypertensive disorders during pregnancy (HDP) have increased risks of preterm birth, fetal growth restriction and several cardiovascular risk factors (e.g., hypertension, obesity, diabetes) later in life. However, the direct evidence on the link between maternal HDP and the risk of severe cardiovascular diseases such as ischemic heart disease (IHD) and stroke in the offspring is very limited. Objective To investigate the associations between maternal HDP and the risk of IHD and stroke in the offspring. Methods We conducted a population-based cohort study by linking several national registers in Sweden and Finland. Live singleton births from the Swedish Medical Birth Register (1973–2014) and the Finnish Medical Birth Register (1987- 2014) were followed for IHD and stroke until 2014 by the national patient and cause of death registers. We performed Cox regression models to examine the association between maternal HDP and its subtypes, i.e., pre-existing chronic hypertension, gestational hypertension, and preeclampsia, and the risk of IHD, and stroke in the offspring while adjusting for relevant maternal and pregnancy-related confounders. We conducted sibling analyses to control for unmeasured shared familial (genetic and/or environmental) risk factors. Results Among the 5,807,122 singletons included in the study, 218,322 (3.76%) children were born to mothers with HDP. During the up to 41 years of follow-up, 2,340 (0.04%) offspring were diagnosed with IHD and 5,360 (0.09%) were diagnosed with stroke. Offspring exposed to maternal HDP had an increased risk of IHD (adjusted hazard ratio (aHR), 1.29; 95% confidence interval (CI), 1.01–1.63), and stroke (aHR,1.33; 95% CI, 1.14–1.56). Significantly increased rates of stroke were also observed in children exposed to the subtypes of maternal HDP: pre-existing chronic hypertension (aHR, 1.64; 95% CI, 1.03–2.60), gestational hypertension (HR, 1.38; 95% CI, 1.08–1.77), and preeclampsia (HR, 1.26; 95% CI, 1.02–1.55). The associations between maternal HDP and offspring's IHD and stroke were independent of preterm birth and small for gestational age at birth. Maternal HDP remained associated with stroke in the offspring (aHR, 1.94; 95% CI, 1.16–3.22), but not with IHD (aHR, 0.89; 95% CI, 0.47–1.67) in the sibling analyses. Conclusion Children to mothers with HDP have increased rates of IHD and stroke from childhood to young adulthood. While the link between maternal HDP and IHD in the offspring seemed to be attributed to confounding by familial factors, the relation between maternal HDP and stroke persisted even when considering such confounding. Persons born to mothers with HDP may benefit from early screening and prevention efforts to reduce the risk of IHD and stroke later in life. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Swedish Heart and Lung Foundation

Alloy design strategy for microstructural-tailored scandium-modified aluminium alloys for additive manufacturing

To exploit the full potential of the additive layer manufacturing technique it is necessary to adapt the material to the process via a smart alloy design strategy. To this end, in order to derive and investigate various material concepts, the microstructural evolution of Sc-modified Al alloys was studied during the course of their production by laser powder bed fusion. Adding Mg as the main element (Al-4.4Mg-0.8Sc-0.3Zr-0.5Mn) generates an already-familiar bimodal microstructure. In contrast, if Cr is added as the main element (Al-2.6Cr-0.7Sc-0.3Zr), epitaxial grain growth takes place across several weld tracks, resulting in a distinct texture; and adding Ti as the main element (Al-1Ti-1Sc-0.4Zr) produces a uniform ultrafine-grained microstructure. The differences between these microstructures arise from interactions of the grain growth restriction factors and the solute with the primary precipitation structure. Thus, the precise manipulation of key metallurgical factors leads to novel materials which can be tailor-made for certain requirements.

The grain refinement of aluminium by a new as-cast Al–Ti–TiCN composite

A new type of composite refiner Ti/TiCN is prepared by loading submicron-TiCN particles onto Ti micron-particles and added to industrial pure aluminium. Refining mechanism has been characterised in detail by optical microscopy, scanning electron microscopy and transmission electron microscopy coupled with energy disperse X-ray spectra. These experimental results show that Ti/TiCN inoculation is more effective in refining pure aluminium than Ti and TiCN added separately. The relationship between grain size and growth restriction factors of aluminium matrix containing Ti/TiCN refiner is d = 70.2 + 1190.8/Q. According to the free growth theory, aluminium matrix with Ti/TiCN inoculation has the largest solidification driving force to promote grain nucleation under the same growth restriction factors (Q = 0.5,1, 5, 12, 20 K) compared to Ti and TiCN refiners.

Microstructures and tensile properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements of Y, Bi, Sb and Sr

The microstructures and mechanical properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements Y, Bi, Sb and Sr were investigated and compared. Results show that the microstructure of the as-cast Mg-5Sn-1Si alloy consists of α-Mg, Mg2Si, Mg2Sn and Mg2(SixSn1−x) phases. After adding 0.8wt.% Y, 0.3wt.% Bi, 0.9wt.% Sb and 0.9wt.% Sr, respectively into the Mg-5Sn-1Si magnesium alloy, Mg24Y5, Mg3Bi2, Mg3Sb2 and Mg2Sr phases are precipitated accordingly. Trace elements can refine α-Mg grain and Chinese script-shaped Mg2Si phase. Refinement efficiency of different trace elements on α-Mg grain and Mg2Si phase is varied. Sr element has the best refinement effect, followed by Sb and Bi, while Y has the least refinement effect. Mg-5Sn-1Si-0.9Sr alloy has higher tensile properties than the other three modified alloys. The refinement mechanism of Y, Bi and Sr elements on Mg-5Sn-1Si magnesium alloy can be explained by the growth restriction factors and the solute undercooling. For Mg-5Sn-1Si-0.9Sb alloy, the heterogeneous nuclei of Mg3Sb2 phase is the main reason for the refinement of grains and second phases.

Designing VxNbMoTa refractory high-entropy alloys with improved properties for high-temperature applications

Poor high/medium-temperature phase stability and/or low room-temperature ductility are currently bottlenecks of refractory high-entropy alloys (RHEAs) that restrict their high-temperature applications. Here, we explored novel VxNbMoTa RHEAs with vanadium concentrations of 0–25 at.%. VxNbMoTa RHEAs exhibit a single body-centered cubic (BCC) structure with unprecedented phase stability at a wide temperature range from solidus down to 350°C. The grain structure of VxNbMoTa can be substantially refined when increasing the V concentration since higher V contents induce stronger solutal effects which contribute to higher growth restriction factors. Equimolar VNbMoTa exhibits the yield strength of 811 MPa at 1000°C that is superior to most RHEAs reported by far, and this alloy also shows excellent room-temperature ductility with the fracture strain > 25% and no strain-softening at high temperature, which is rarely seen in many popular RHEAs. These exceptional performances of VNbMoTa enable it to be a very promising material for high-temperature applications.

Etiology of second-trimester oligohydramnios: a review

The second-trimester oligohydramnios can be caused by various factors. Oligohydramnios is associated with adverse pregnancy outcomes. With the development of clinical detection, there was some progress on investigation of the etiology of second-trimester oligohydramnios. Some inheritable diseases associated with oligohydramnios were discovered. Second-trimester oligohydramnios is associated with fetal abnormalities, fetal growth restriction, and fetal, umbilical cord, maternal, or drug factors. Besides them, renal tubular dysgenesis, an autosomal recessive disorder, might be another associated factor of second-trimester oligohydramnios. Birth defects can be avoided by clarifying the etiology of second-trimester oligohydramnios, and the instruction for further pregnancies. Since the etiology of second-trimester oligohydramnios is still unclear, more clinical, pathological and genetic researches are needed. Key words: Oligohydramnios; Pregnancy trimester, second

Role of ultrasonic treatment, inoculation and solute in the grain refinement of commercial purity aluminium

The present study investigates the influence of ultrasonic treatment on the grain refinement of commercial purity aluminium with a range of Al3Ti1B master alloy additions. When the aluminium contains the smallest amount of added master alloy, ultrasonics caused significant additional grain refinement compared to that provided by the master alloy alone. However, the influence of ultrasonics on grain size reduces with increasing addition of the master alloy which adds additional TiB2 particles and Ti solute with each incremental addition. Applying the Interdependence model to analyse the experimentally measured grain sizes revealed that the results of this study and those from similar experiments on an Al-2Cu alloy were consistent when the alloy compositions are converted to their growth restriction factors (Q) and that increasing Q had a major effect on reducing grain size and increasing grain number density. Compared with the application of ultrasonic treatment where an order of magnitude increase in the grain number density is achieved, an increase in the Ti content over the range of master alloy additions, causes the grain number density to increase by approximately three times.

Impact of Growth Restriction and Other Prenatal Risk Factors on Cord Blood Iron Status in Prematurity.

To determine whether prenatal risk factors (RFs) that predict cord blood iron status in term newborns also predict iron status of premature newborns. Cord blood iron indices from 80 preterm newborns were compared with historical and demographic RFs for developing iron deficiency if born at term. The presence of multiple RFs did not incrementally interfere with cord iron status in preterm newborns. Poorer iron status accompanied being small for gestational age in prematurity, but other RFs, including diabetes, had relatively little impact. Growth-restricted preterm newborns are at risk for poor iron endowment, likely due to uteroplacental insufficiency. Other RFs were less impactful on iron status of premature newborns than in term newborns, likely reflecting that disruptive effects of RFs are more impactful in the third trimester. Understanding RFs for poor iron endowment is important for clinical recognition and treatment of premature babies.

Placental pathologic changes of maternal vascular underperfusion in bronchopulmonary dysplasia and pulmonary hypertension

IntroductionBronchopulmonary dysplasia (BPD) is the most common chronic lung disease of infancy, and BPD-associated pulmonary hypertension (PH) is a serious complication that can negatively impact later childhood health. There is growing evidence that lung injury leading to BPD and PH is due to chronic fetal hypoxia-ischemia. The purpose of this study was to investigate whether placental pathologic changes of maternal vascular underperfusion (MVU) are associated with BPD, and further increased with PH. MethodsWe conducted a 5-year retrospective cohort study of premature infants born ≤28 weeks. BPD was defined as persistent oxygen requirement at 36 weeks corrected gestational age. PH was identified using a standardized algorithm of echocardiogram review. Archived placental slides underwent standardized masked histopathologic review. Logistic regression modeling was performed, taking into account important maternal and infant covariates. ResultsAmong 283 births, 121 had MVU, of which 67 (55%) developed BPD, and 24 (20%) had PH. Among the common neonatal complications of extreme prematurity, BPD was the only outcome that was increased with MVU (P < 0.001). After adjustment for birth weight, fetal growth restriction, preeclampsia and other factors, infants with MVU were more likely to develop BPD (adjusted odds ratio = 2.6; 95% confidence interval = 1.4, 4.8). Certain MVU sublesions (fibrinoid necrosis/acute atherosis and distal villous hypoplasia/small terminal villi) were increased with PH (P < 0.001). DiscussionPlacental MVU may identify BPD infants who were exposed to intrauterine hypoxia-ischemia, which increases their risk for development of PH disease. ConclusionsOur findings have important implications for providing earlier and more effective therapies for BPD.

First trimester fetal growth restriction and cardiovascular risk factors in school age children: population based cohort study

Objective To examine whether first trimester fetal growth restriction correlates with cardiovascular outcomes in childhood.Design Population based prospective cohort study.Setting City of Rotterdam, the Netherlands.Participants 1184 children with first trimester...

Do very preterm twins and singletons differ in their neurodevelopment at 5 years of age?

ObjectiveTwins have inconsistently shown poorer outcomes than singletons. Although a high proportion of twins are born very preterm, data are sparse on the long-term outcomes in very preterm twins. The...

Doppler Sonography in Obstetrics

ABSTRACT Doppler sonographic applications in pregnancy are the widely accepted functional methods of evaluating fetal wellbeing. Flow velocity waveforms provide important information from the early stages of pregnancy to term. Doppler ultrasound is a noninvasive technique whereby the movement of blood is studied by detecting the change in frequency of reflected sound. This method became an important tool for qualifying pregnancies in risk. Information obtained with Doppler sonography helps obstetricians managing patients in situations like pregnancies complicated by intrauterine growth restriction (IUGR), rhesus alloimmunization, multiple pregnancies and anamnestic risk factors. Examination of the uteroplacental and fetomaternal circulation by Doppler sonography in the early second trimester helps predicting pregnancy complications like preeclampsia, IUGR and perinatal death. This chapter aims to discuss Doppler sonographic examinations in modern obstetrics. To date, randomized controlled trials were able to establish important clinical value of Doppler velocimetry in obstetrics to improve perinatal outcome in highrisk situations. How to cite this article Ertan AK, Taniverdi HA. Doppler Sonography in Obstetrics. Donald School J Ultrasound Obstet Gynecol 2013;7(2):128-148.

Obstetric Ultrasound: Errors and Pitfalls in Fetal Growth Restriction

IntroductionUltrasound is a method of tracking deviations fetal growth. In 75% of cases of fetal growth restriction (CIR), biological or constitutional factors are associated.Methods InvolvedThe cases were selected retrospectively from the personal archive of the authors, cases and situations experienced that can lead to misinterpretation by the sonographer on suspicion of CIR in order to discuss the sonographic diagnostic criteria.DiscussionThe triad: amniotic fluid, placenta and fetal movement activates normal are great indicators to rule out other etiologies involved in the genesis of the CIR. The normal fetal morphology is important to exclude malformations and chromosomal defects that cause the CIR also symmetrical. The fetuses with growth restriction of symmetrical (fetal weight below the 10th percentile for gestational age referred to) have different etiologies and may be maternal (congenital infections, chromosomal disorders, chromosomal abnormalities not like gastroschisis, irradiation, teratogenic drugs) or constitutional.Conclusion of the PresentationThe sonographic identification of fetal weight below the 10th percentile for gestational age that should trigger the search for possible etiologies involved in low fetal weight. However, it is important biological and constitutional rule, which accounts for most cases, so that there is no premature termination of pregnancy. IntroductionUltrasound is a method of tracking deviations fetal growth. In 75% of cases of fetal growth restriction (CIR), biological or constitutional factors are associated. Ultrasound is a method of tracking deviations fetal growth. In 75% of cases of fetal growth restriction (CIR), biological or constitutional factors are associated. Methods InvolvedThe cases were selected retrospectively from the personal archive of the authors, cases and situations experienced that can lead to misinterpretation by the sonographer on suspicion of CIR in order to discuss the sonographic diagnostic criteria. The cases were selected retrospectively from the personal archive of the authors, cases and situations experienced that can lead to misinterpretation by the sonographer on suspicion of CIR in order to discuss the sonographic diagnostic criteria. DiscussionThe triad: amniotic fluid, placenta and fetal movement activates normal are great indicators to rule out other etiologies involved in the genesis of the CIR. The normal fetal morphology is important to exclude malformations and chromosomal defects that cause the CIR also symmetrical. The fetuses with growth restriction of symmetrical (fetal weight below the 10th percentile for gestational age referred to) have different etiologies and may be maternal (congenital infections, chromosomal disorders, chromosomal abnormalities not like gastroschisis, irradiation, teratogenic drugs) or constitutional. The triad: amniotic fluid, placenta and fetal movement activates normal are great indicators to rule out other etiologies involved in the genesis of the CIR. The normal fetal morphology is important to exclude malformations and chromosomal defects that cause the CIR also symmetrical. The fetuses with growth restriction of symmetrical (fetal weight below the 10th percentile for gestational age referred to) have different etiologies and may be maternal (congenital infections, chromosomal disorders, chromosomal abnormalities not like gastroschisis, irradiation, teratogenic drugs) or constitutional. Conclusion of the PresentationThe sonographic identification of fetal weight below the 10th percentile for gestational age that should trigger the search for possible etiologies involved in low fetal weight. However, it is important biological and constitutional rule, which accounts for most cases, so that there is no premature termination of pregnancy. The sonographic identification of fetal weight below the 10th percentile for gestational age that should trigger the search for possible etiologies involved in low fetal weight. However, it is important biological and constitutional rule, which accounts for most cases, so that there is no premature termination of pregnancy.

Perfil lipídico na adolescência: efeito de exposições intra-uterinas

This study assessed the effects of intrauterine growth restriction and risk factors for intrauterine growth restriction on blood lipids in adolescents from the 1982 birth cohort in Pelotas, Rio Grande do Sul State, Brazil. All male subjects were identified in 2000 when enrolling in the national army; 79% (n = 2,250) were interviewed, and 2,089 provided blood samples. The following outcome variables were studied: total cholesterol and fractions (VLDL, LDL, and HDL), non-HDL cholesterol, LDL/HDL ratio, and serum triglycerides. The explanatory variables were intrauterine growth restriction, maternal pre-gestational body mass index (BMI), and maternal smoking during pregnancy. After adjusting for confounding variables, total, LDL, and non-HDL cholesterol levels were slightly and significantly higher among adolescents whose mothers were in the 3rd and 4th quartiles of pre-gestational BMI. However, these associations disappeared after adjusting for the adolescent's diet, schooling, and BMI. Other associations were not significant (p > 0.05).

Segregation and grain refinement in cast titanium alloys

The growth restriction factor is a parameter derived from binary phase diagrams and is a useful predictor for the grain refining response when a solute is added to a base alloy. This work investigates the relevance of growth restriction theory to titanium alloys where solidification rates are an order of magnitude faster than previous studies in aluminum- and magnesium-based systems. In particular, the segregation of Fe and Cr in titanium is investigated and the effects on grain size studied. It was found that the Scheil equation reasonably modeled solidification of titanium where cooling rates approach 120 °C/s, and the growth restriction factors for Fe and Cr were useful in predicting prior-β grain refinement. However, it was found that caution must be used when calculating growth restriction factors from binary phase diagrams.