Soft Impingement Research Articles

Short study on mechanism of morphology change of γ′ precipitates in IN718 Plus

γ′ Ni3Al phase (L12 structure) strengthened superalloy has become an important strengthening phase in Ni based superalloys because of its excellent high-temperature service performance, and has been widely used. The process of γ′ phase precipitation has also received a lot of attention and research. However, most studies focused on its growth rate. There were few studies on the morphology transformation of γ′ phase, and the morphology transformation process is complex. The mechanism of γ′ phase transformation process was systematically analyzed in this paper. Firstly, through molecular dynamics calculation, the most stable morphology of the γ′ phase in the nickel matrix was obtained under ideal conditions. The stability of spherical precipitates is higher than that of cubic precipitates. When the temperature is greater than 800 K, the stability is more obvious.Then through the micro EDS analysis of the γ′ phase in the morphology transformation process, it was shown that the soft impingement phenomenon exists in the nickel base alloy with high γ′ phase volume fraction. Further, by the derivation of the formula of solid-state phase transformation, it was found that the growth rate of precipitate is directly proportional to the concentration gradient of Al in the matrix at the interface, while increases with the rising of the Al concentration in the matrix at the interface. Finally, the way and mechanism of soft impingement affecting the morphology transformation were analyzed. The precipitates formed by soft impingement are nearly cubic precipitates with rounded edges and corners.

Soft Tissue Cam Impingement in Adolescents: MRI Reveals Impingement Lesions Underappreciated on Radiographs

Background: Femoroacetabular impingement (FAI) has been described as repetitive and abnormal contact between a structurally abnormal proximal femur (cam) and/or acetabulum (pincer), occurring during the terminal range of motion of the hip. While cam and pincer lesions have traditionally been defined as osseous abnormalities, there may be a subset of adolescent patients whose impingement is primarily soft tissue (nonosseous). The existence of a nonosseous cam lesion in adolescents with FAI has not been well described. Purpose: To identify and characterize a series of adolescent patients with nonosseous (soft cam) FAI identified on magnetic resonance imaging (MRI) and compare these patients’ clinical presentation and outcome with those of a cohort with primary osseous cam FAI in the same age group. Study Design: Case series; Level of evidence, 4. Methods: A prospective institutional registry of patients with symptomatic FAI was reviewed. Patients were included if they had an MRI scan and a lateral radiograph of the hip (45° Dunn or frog) at a baseline visit. On MRI, the anterolateral femoral head was evaluated using radial, coronal, sagittal, or axial oblique sequences. A soft cam lesion was identified by the presence of soft tissue thickening of ≥2 mm at the anterolateral femoral head-neck junction. An alpha angle was measured on MRI scans and radiographs when a lesion was identified. The cohort with soft cam lesions was reviewed and findings and outcomes were compared with those of a cohort with osseous cam lesions. Continuous variables were first examined for normality, and then nonparametric tests—such as the Kruskal-Wallis test—were considered. The change between pre- and postoperative patient-reported outcomes (PROs) was described by mean and standard deviation and evaluated with an independent-samples t test. Results: A total of 31 (9.3%) of 332 hips (mean age, 16.4 years [range 13.1-19.6 years]; women, 83.9%) were identified with a soft tissue impingment lesion on MRI at the femoral head-neck junction between the 12 and 3 o'clock positions. These lesions demonstrated a thickened perichondral ring (71%), periosteal thickening (26%), or a cartilaginous epiphyseal extension (3%). The mean alpha angle on MRI was greater than on radiographs (63.5°± 7.9° vs 51.3°± 7.9°; P < .0001). A total of 22 patients (71%) with soft impingement underwent hip preservation surgery. When compared with patients in the osseous cohort who also underwent surgical management, both groups showed similar significant improvements from pre- to postoperatively (soft: modified Harris Hip Score [mHHS], 26.9 ± 18.2; Hip disability and Osteoarthritis Outcome Score [HOOS], 31.4 ± 22.9; osseous: mHHS, 22.8 ± 20.8; HOOS, 27.4 ± 20.1; P < .0001), with a mean follow-up of 3.4 years (range, 1-7 years) in the soft cam cohort and 3 years (1-10.1 years) in the osseous cam cohort. Conclusion: Clinicians should be aware of nonosseous or soft cam lesions that cause impingement in adolescent patients without an obvious osseous cam on radiographs. MRI is required to detect these soft cam lesions. When nonoperative treatment fails, the PROs in these patients after operative management are comparable with those in patients with osseous cam lesions. Further research is needed to determine whether the soft cam precedes an osseous cam or whether it is a separate entity.

Can ultrasound replace MRI in diagnosing causes of ankle impingement in different compartments?

This prospective study aims to determine the role of ultrasound (US) in diagnosing different types of ankle impingement due to osseous and soft tissue pathologies and to compare the results with magnetic resonance imaging (MRI), which is considered our gold standard. The study population included 90 patients with unilateral ankle pain who presented with symptoms and signs suggestive of ankle impingement. Their age ranged from 17 to 57years, with a mean age of 33.7years. Using US and MRI, our cases were classified into bony and soft tissue ankle impingement. They were further classified according to the anatomical compartments affected, into anteromedial, anterior, anterolateral, posteromedial, and posterior. 90 patients were enrolled in this study: 51 males and 39 females. In our study, posterior ankle impingement was the commonest impingement type, while anteromedial ankle impingement was the rarest type, followed by posteromedial impingement. The accuracy of US in diagnosing osseous impingement was found to have the following: sensitivity 70.37%, specificity 100%, PPV 100%, NPV 75%, accuracy 84.31%, and p value < 0.001; meanwhile, the accuracy of US in diagnosing soft tissue impingement was found to have the following: sensitivity 83.33%, specificity 100%, PPV 100%, NPV 87.10%, accuracy 92.16%, and p value < 0.001. US is a good diagnostic tool in bone and soft tissue impingements, with a significant p value of 0.001 for both. US cannot replace MRI as a diagnostic tool, but as a widely available imaging modality, it can save time and cost and allows dynamic imaging.

Phase transformation and growth mechanism of RF sputtered ferroelectric lead scandium tantalate (PbSc0.5Ta0.5O3) films

AbstractLead scandium tantalate (PbSc0.5Ta0.5O3, PST), an order/disorder ferroelectric, is a potential candidate for electrocaloric cooling and pyroelectric infrared (IR) detector. In this work, we report the phase transformation kinetics from two series of samples containing pure amorphous and mixture of amorphous and pyrochlore to desired perovskite phase using postdeposition rapid thermal processing (RTP) as well as growth mechanism of RF sputtered PST thin films using excess lead target on platinized silicon (Pt/Ti/SiO2/Si) substrates. We find that small changes in the temperature ramp have a large effect on the degree of perovskite conversion (ferroelectric phase), orientation (crystallographic texture), and long‐range order parameter (&lt; S111 &gt;). Through isothermal annealing, we obtained optimal perovskite phase at ≥700°C temperature. The phase transformation is characterized by spontaneous formation of center‐type in‐plane radial rosette‐like structures revealed by scanning electron microscopy. The PST perovskite crystallites were found to coexist with pyrochlore in RTP annealed films. The volume fractions for perovskite and pyrochlore phase were obtained from the analysis of “rosettes” and respective X‐ray diffraction intensities which helped to determine various parameters associated with phase kinetics (n, k, and activation energy, Ea) and accompanying growth. The effective activation energies of perovskite transition and growth were found to be 332 ± 11 kJ/mol (345 ± 11 kJ/mol) and 114 ± 10 kJ/mol (122 ± 10 kJ/mol), respectively, for pure amorphous only (and mixed amorphous and pyrochlore) phase following nucleation‐growth controlled Avrami's equation. A linear growth rate (n∼1) for the perovskite phase indicates predominant interface‐controlled process and diffusion‐limited phenomena thus inhibiting rosette size owing to reactant depletion and soft impingement at the grain boundary. However, the growth behavior is isotropic in two‐dimension parallel to the plane of the substrates for both sample series. Lead loss was severe for in‐situ growth and RTP combined with conventional furnace annealing than those of RTP only films, which were closer to stoichiometric albeit with excess lead and marginal oxygen vacancies (Vo).

Computed tomography–based three-dimensional modeling of glenoid bone preservation with augmented baseplates

BackgroundReverse total shoulder arthroplasty (rTSA) is a treatment option for a variety of shoulder pathologies, including rotator cuff arthropathy, glenohumeral arthritis, and irreparable rotator cuff tears and fractures. There has been substantial improvement in rTSA implants and surgical techniques, such as augmented baseplates that preserve bone tissue. In this study, we used three-dimensional modeling to determine the extent of bone preservation with augmented baseplates in rTSA. MethodsComputed tomography scans from 50 consecutive patients before they underwent rTSA were used to create three-dimensional models of each glenoid. The virtual positions of reverse shoulder baseplate implants followed strict parameters for adequate fixation as determined through consensus among 4 fellowship-trained shoulder specialists. Parameters for adequate fixations included 100% backside contact, neutral scapular version, and 10° of inferior tilt. The 4 baseplate options trialed on each glenoid were a nonaugmented baseplate, a small 10° half-wedge augment, a medium 20° half-wedge augment, and a large 30° half-wedge augment. The extent of volumetric glenoid bone removal and lateralization of the baseplate was calculated for each scenario. ResultsPreoperative computed tomography imaging showed a mean of 10.7° of retroversion and a reverse shoulder arthroplasty angle of 21.3°. A medium augment (20° half wedge) was determined as optimal in 29 cases, and a large augment (30° half wedge) was considered optimal for the remaining 21 cases. The use of augmented baseplates was calculated to preserve 54% glenoid bone stock (1989 ± 650 mm3 bone removal vs. 4439 ± 1636 mm3 with nonaugmented baseplate; P < .001). The surgeon-selected augmented baseplate was on average 4.1 mm lateral in comparison to the nonaugmented baseplate. ConclusionsThe use of augmented baseplates reduces the volume of bone that needs to be removed in rTSA. Furthermore, augmented baseplates result in relative lateralization of the glenosphere, which has been theorized to improve soft tissue tension and limit impingement and scapular notching. Further exploration of the impact of augmented baseplates on clinical outcomes is needed.

Soft Tissue CAM Impingement in Adolescents: MRI reveals impingement lesions underappreciated on x-ray (138)

Objectives:The presence of femoroacetabular impingement (FAI) in adolescents has been established. However, the existence of a non-ossified CAM lesion in adolescent femoracetabular impingement (FAI) is not well described. The purpose of this study is to evaluate the presence of a non-ossified or soft CAM lesion in adolescent patients with FAI.Methods:A review of a prospective cohort of patients with symptomatic FAI in an institutional registry was performed. Subjects were included if they had an MRI and lateral x-ray of the hip (45o Dunn, Cross Table, or frog) at a baseline visit. On MRI, evaluation of the anterolateral femoral head was evaluated using radial, coronal, sagittal, or axial oblique sequences. When a soft CAM lesion was identified (all found between 2-5 o’clock), an alpha angle was performed on MRI and plain radiograph. The cohort of soft CAM lesions was reviewed and differences between radiographic and MRI alpha angles were assessed using a paired T-Test.Results:Thirty-one (9.3%) of 332 hips (mean age 16.4 yrs, range 13.66-19.59 yrs; 83.9% F) were identified with a soft impinging lesion at the femoral head-neck junction on MRI. The most common primary sport was track & field (4), the average duration of symptoms was 92.4 weeks and a majority with insidious onset (77.4%). The average alpha angle on MRI was greater than on x-ray [63.53 ± 7.94o vs 51.25 ± 7.92o; p<.05]. All subjects with soft CAM lesions demonstrated soft tissue consistent with extension of the physis (n=1),thickening of the peri-chondral ring (n=22), or thickening of the periosteum (n=8). Twenty-two of these patients (71%) with soft impingement underwent hip preservation surgery (n=13 labral repairs) with improvements in clinical outcome.Conclusions:In adolescent patients with symptomatic hip impingement, MRI may be useful to identify soft CAM lesions (non-ossified) that are under-represented on x-ray.

Effect of tantalum on the microstructure stability of PM Ni-base superalloys

The effect of Ta on the microstructure stability of powder metallurgy (PM) Ni-base superalloy was examined at standard heat treatment and after long-term thermal exposure. The results reveal that the previous particle boundary structure is eliminated with the addition of Ta. As Ta content increases, the γ' morphology changes from spheres to cuboids and begins to split, which is caused by the increase in the γ/γ' mismatch. Reversal coarsening of γ' particles in Ta-containing alloys are observed during exposure at 750 °C. The main reasons are related to γ/γ' lattice mismatch, elements partitioning and soft impingement. Besides, the increase of Ta content promotes the precipitation of σ phase at grain boundaries and in grains. • The PM Ni-based superalloys were fabricated by plasma rotation electrode process and hot isostatic pressing. • Systematical study on microstructure evolution of the PM superalloy with increase of Ta content. • The addition of Ta effectively inhibits the previous particle boundary structure in PM superalloy. • The addition of Ta changes the partitioning of alloying elements in γ and γ'. • Reversal coarsening of γ' particles occurred in the Ta-containing alloys during the aging at 750 °C.

SOFT TISSUE CAM IMPINGEMENT IN ADOLESCENTS: MRI REVEALS IMPINGEMENT LESIONS UNDERAPPRECIATED ON X-RAY

Background:The presence of femoroacetabular impingement (FAI) in adolescents has been established. However, the existence of a non-ossified CAM lesion in adolescent femoracetabular impingement (FAI) is not well described.Hypthesis/Purpose:The purpose of this study is to evaluate the presence of a non-ossified or soft CAM lesion in adolescent patients with FAI.Methods:A review of a prospective cohort of patients with symptomatic FAI in an institutional registry was performed. Subjects were included if they had an MRI and lateral x-ray of the hip (45o Dunn, Cross Table, or frog) at a baseline visit. On MRI, evaluation of the anterolateral femoral head was evaluated using radial, coronal, sagittal, or axial oblique sequences. When a soft CAM lesion was identified (all found between 2-5 o’clock), an alpha angle was performed on MRI and plain radiograph. The cohort of soft CAM lesions was reviewed and differences between radiographic and MRI alpha angles were assessed using a paired T-Test.Results:Thirty-one (9.3%) of 332 hips (mean age 16.4 yrs, range 13.66-19.59 yrs; 83.9% F) were identified with a soft impinging lesion at the femoral head-neck junction on MRI. The most common primary sport was track & field (4), the average duration of symptoms was 92.4 weeks and a majority with insidious onset (77.4%). The average alpha angle on MRI was greater than on x-ray [63.53 ± 7.94o vs 51.25 ± 7.92o; p<0.05]. All subjects with soft CAM lesions demonstrated soft tissue consistent with extension of the physis (n=1),thickening of the peri-chondral ring (n=22), or thickening of the periosteum (n=8). Twenty-two of these patients (71%) with soft impingement underwent hip preservation surgery (n=13 labral repairs) with improvements in clinical outcome.Conclusion:In adolescent patients with symptomatic hip impingement, MRI may be useful to identify soft CAM lesions (non-ossified) that are under-represented on x-ray.

Precipitation and Growth Simulation of γ′ Phase in Single Crystal Superalloy DD6 with Multiphase-Field Method and Explicit Nucleation Algorithm

The microstructure evolution of Ni-based superalloys during heat treatment is of great significance for obtaining better service performance. However, heat treatment experimentation is costly and time-consuming, and sometimes fails to reveal physical mechanisms well. In the present study, a multiphase-field model coupled with an explicit nucleation algorithm was established to simulate the precipitation and growth of γ′ phase in DD6 superalloy, which can be applied to a multicomponent elastic-inhomogeneous system. The PanNickel© database was used to calculate thermodynamic and kinetic data in multicomponent superalloys. First, the coupling method of multiphase-field model and explicit nucleation algorithm was introduced. The coupled model was used to simulate the precipitation of γ′ phase under isothermal and non-isothermal conditions. It was found that a unimodal microstructure was formed under isothermal conditions and there was a “soft impingement” phenomenon, while a bimodal distribution composed of cuboidal γ′ precipitates and fine secondary γ′ precipitates was formed during a cooling process of 25–125 °C/min. The effect of cooling rate was studied. Then, the chemical and elastic driving forces were analyzed. It was found that Al and Ta contributed most to the chemical driving force, while Re and W gathered at the γ/γ′ interface and inhibited the growth of γ′ phase. γ′ precipitates had a cuboidal shape under the influence of elastic driving force. Finally, the growth and coarsening process of γ′ phase was studied and compared with the well-known Lifshitz−Slyosov−Wagner (LSW) theory. The growth of γ′ phase can be divided into rapid growth, coarsening and quasi-static coarsening stages according to the simulation results, among which the coarsening stage is basically consistent with the LSW theory. The current model can be used to simulate the precipitation and growth of single crystal superalloys where multicomponent and elastic effects are considered.

Arthroscopic Treatment of Anterior Ankle Impingement

Background and objectives:Anterior ankle impingement (as a common cause of anterior ankle pain) is becoming re- cently a common diagnosis in peoples who do excessive dorsiflexion of ankle joint in their daily activities. Arthroscopic debridement is nowadays a gold standard procedure for anterior ankle impingement treatment in both osseous and soft tissue type impingements. The objectives of this study are to provide a comprehensive overview of the clinical outcomes of arthroscopic procedures used as a treatment strategy for anterior ankle impingement. Methods:We per- formed a prospective study on 20 patients diagnosed as cases of anterior ankle impingement on the basis of clinical and radiological examination, the patients complained from either soft tissue or bony impingement. All patients were treated by arthroscopic debridement or burring. Clinical outcome was evaluated according to American orthopedic foot and ankle society score questionnaires, visual analogue scale, and ankle dorsiflexion range achieved. Results: The mean age of the patients was 37.4 year, mean AOFAS ankle hind-foot scale improved from 52.65 preoperatively to 86.95 postoperatively (statistically significant). The mean pain visual analogue scale decreased from 7.9 to 3.1. The mean dorsiflexion angle increased from 7 degrees to 14.5 degrees. Conclusion: Arthroscopic debridement and excision of impinging soft tissues and burring of impinging bones is the treatment of choice for patients with anterior ankle impingement syndrome of both osseous and soft tissue nature after failure of conservative measures to relieve the symptoms and improve the range of motion.

The Kinetics of Primary Alpha Plate Growth in Titanium Alloys

The kinetics of primary α-Ti colony/Widmanstätten plate growth from the β are examined in Ti-6246, comparing a simple quasi-analytic model to experiment. The plate growth velocity depends sensitively both on the diffusivity D(T) of the rate-limiting species and on the supersaturation around the growing plate. These result in a maxima in growth velocity around 40 K below the transus, once sufficient supersaturation is available to drive the plate growth. In Ti-6246, the plate growth velocity was found to be around 0.32 μm min−1 at 850 °C, which was in good agreement with the model prediction of 0.36 μm min−1. The solute field around the growing plates, and the plate thickness, was found to be quite variable, due to the intergrowth of plates and soft impingement. This solute field was found to extend to up to 30 nm, and the interface concentration in the β was found to be around 6.4 at. pct Mo. It was found that the increasing O content from 500 to 1500 wppm will have minimal effect on the plate lengths expected during continuous cooling; in contrast, Mo approximately doubles the plate lengths obtained for every 2 wt pct Mo reduction. Alloys using V as the β stabilizer instead of Mo are expected to have much faster plate growth kinetics at nominally equivalent V contents. These findings will provide a useful tool for the integrated design of alloys and process routes to achieve tailored microstructures.

Interaction of precipitation with austenite-to-ferrite phase transformation in vanadium micro-alloyed steels

The precipitation kinetics of vanadium carbides and its interaction with the austenite-to-ferrite phase transformation is studied in two micro-alloyed steels that differ in vanadium and carbon concentrations by a factor of two, but have the same vanadium-to-carbon atomic ratio of 1:1. Dilatometry is used for heat-treating the specimens and studying the phase transformation kinetics during annealing at isothermal holding temperatures of 900, 750 and 650 °C for up to 10 h. Small-Angle Neutron Scattering (SANS) and Atom Probe Tomography (APT) measurements are performed to study the vanadium carbide precipitation kinetics. Vanadium carbide precipitation is not observed after annealing for 10 h at 900 and 750 °C, which is contrary to predictions from thermodynamic equilibrium calculations. Vanadium carbide precipitation is only observed during or after the austenite-to-ferrite phase transformation at 650 °C. The precipitate volume fraction and mean radius continuously increase as holding time increases, while the precipitate number density starts to decrease after 20 min, which corresponds to the time at which the austenite-to-ferrite phase transformation is finished. This indicates that nucleation and growth are dominant during the first 20 min, while later precipitate growth with soft impingement (overlapping diffusion fields) and coarsening take place. APT shows gradual changes in the precipitate chemical composition during annealing at 650 °C, which finally reaches a 1:1 atomic ratio of vanadium-to-carbon in the core of the precipitates after 10 h.

The Role of Ultrasound Imaging in Ankle Impingement

AbstractBackground: Ankle impingement is a clinical condition of chronic and painful limited range of joint movement. It presents a significant clinical concern athletes and young population.Aim of Study: To study the value of US in the diagnosis of soft tissue and bony ankle impingement, using combined plain radiography and MRI as a reference for diagnosis.Patients and Methods: The study included 20 patients (8 male and 12 female), mean age: 35. 1 years, suspected to have ankle impingement by clinical examination. The included patients underwent US ankle examination. The diagnosis of impingement was classified according to the anatomical compartments and categorized according to the underlying impinging factor as bony or soft tissue impingement. We calculated a p-value to evaluate the role of US in diagnosis of bone and soft tissue impingement.Results: Eight patients had single compartment impinge-ment and 12 patients (60%) had multi-compartments impinge-ment with a total number of 40 compartments impingement. The observed impingements were categorized into 22 soft tissue and 18 bone impingements. Ultrasound could detect 11 out of 18 bone impingements (p-value=0.011) and 21 out of 22 soft tissue impingements (p-value=0.005).Conclusion: Ultrasound is a helpful diagnostic tool in cases of bone and soft tissue ankle impingement.

Formation mechanism of lamellar alpha in titanium through accurate simulation

The lamellar α, transformed β matrix and spheroidization products of them combine to form all typical microstructures in titanium alloys. Accurately predicting the formation of lamellar α and revealing the precipitation mechanism therefore become vital for tailoring the microstructure and thus optimizing the properties of titanium alloys. A mixed-mode model combined with cellular automaton is proposed to simulate the process of nucleation and growth of lamellar α phase in isothermal treatment of Ti alloys. In this model, the driving force that is dependent on temperature, the solute concentration in two phases and interface is derived; the soft impingement effect, considering the microscopic morphology evolution of lamellar α phase in two dimensions, is well described by not only approximating the diffusion field function in front of the interface as a polynomial but also introducing the area and interface length of lamellar α into the mass conservation law. A comparision with the interface-controlled and diffusion-controlled models shows that the mixed-mode model gives obviously more accurate description of β-to-α phase transformation kinetics. Furthermore, it is also found that the interfacial migration coefficient, and the microscopic morphology of lamellar α phase to be precipitated have great effects on the mixed mode character (in especial the change in controlled mode) and the kinetics of entire phase transformation process.

Void evolution in tungsten and tungsten-5wt.% tantalum under in-situ proton irradiation at 800 and 1000 °C

We have probed void evolution in polycrystalline W and W-5wt.%Ta material at 800 and 1000 °C, by transmission electron microscopy during in-situ irradiation with a 40 keV proton beam. The presence of radiation-induced dislocation loops was not observed prior to void formation at those elevated temperatures. The damaged W microstructure was characterised by the presence of a population of randomly distributed voids, whose number density reduces when the irradiation temperature increases. Soft impingement of voids becomes noticeable at damage levels ≥0.2 dpa. In contrast, the excess of free vacancies in the W-5wt.%Ta material irradiated at 800 °C only leads to the formation of visible voids in this TEM study (≥2 nm) after post-irradiation annealing of the sample at 1000 °C. Solute Ta atoms also cause a significant increase in the number density of voids when comparing the microstructure of both materials irradiated at 1000 °C, and a gradual progression towards saturation in average void size at ≥0.2 dpa. Moreover, we have detected a progressive transition from a spherical to a faceted shape in a number of voids present in both materials at damage levels ≥0.3 dpa.

Phase transformation mechanisms during Quenching and Partitioning of a ductile cast iron

The modification of the matrix of ductile cast irons by heat treatments has been of interest of researchers for many years. Among these treatments, in the last years the Quenching & Partitioning (Q&P) process has emerged as a viable way to produce microstructures containing controlled amounts of martensite and retained austenite, providing a good combination of strength and ductility. In this work, the different mechanisms of phase transformations occurring during the Q&P heat treatment applied to a ductile cast iron alloy is investigated. Microsegregation, inherent to cast irons, was analyzed by means of Electron Probe Microanalysis (EPMA). Microstructural characterization was performed with Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD), while kinetics of carbon redistribution and competitive reactions were studied using dilatometry and in situ synchrotron X-ray diffraction. It was found that either transition carbides or cementite precipitate in martensite depending on the partitioning temperature. Despite of carbides precipitation, evidence of carbon partitioning from martensite to austenite was obtained. Formation of bainitic ferrite occurs during the partitioning step, further contributing to carbon enrichment of austenite. The experimental results are compared with a local field model that computes the local kinetics of carbon redistribution by simultaneously considering carbides precipitation and growth of bainitic ferrite. Results showed that kinetics of carbon partitioning from martensite to austenite depends on the carbides free energy. More stable carbides do not dissolve and prevent the escape of carbon from martensite. Fast carbon partitioning occurs by dissolution of less stable carbides, but it is slowed down as growth of bainitic ferrite proceeds. This result is explained by the overlapping of the diffusion fields (soft impingement) of the carbon partitioned from martensite and the carbon rejected from growth of bainitic ferrite.

A Gibbs Energy Balance Model for Growth Via Diffusional Growth-Ledges

Growth ledges are commonly observed on interphase boundaries during diffusional phase transformations and are of great importance for understanding inter-sheet spacing of interphase precipitates. A simple model based on Gibbs Energy Balance (GEB) for describing growth kinetics via diffusional growth-ledges of height λ is presented for the case of ferrite growth into austenite. The model is validated against the case of austenite to ferrite transformation involving interphase precipitation in a V, Mn, Si alloyed HSLA steel where, λ is assumed to be equal to the inter-sheet spacing of interphase carbide precipitates. The presented model provides a computationally efficient and versatile method for predicting the ledge height, λ, and the growth kinetics of ferrite from initial nucleation through to final soft impingement considering the evolution of solute drag at growth ledge risers. It is suggested that the intrinsic mobility of growth ledge risers is: M_{m}^{aR} = 0.58(exp\frac{-140x10^{3}{RT})mmol.J^{-1}s^{-1}, with R the gas constant and T the absolute temperature in K.

Dissolution of the Alpha Phase in Ti-6Al-4V During Isothermal and Continuous Heat Treatment

The kinetics of the dissolution of the equiaxed alpha phase into the beta matrix in Ti-6Al-4V were established and modeled for both isothermal (constant temperature) and transient/continuous heating conditions. For the isothermal experiments, samples were solution treated at a subtransus temperature to equilibrate the microstructure followed by rapid, direct-resistance heating to a temperature either 25 K or 78 K (25 °C or 78 °C) above the equilibrium beta transus and held for times ranging from 1 to 32 seconds. Dissolution behavior under transient conditions was determined in-situ using an indirect-resistance furnace and X-ray (synchrotron) source; these trials comprised a similar initial subtransus solution heat treatment followed by continuous heating at a constant rate in the range between 15 and 135 K/min (15 and 135 °C/min) to a temperature lying 25 K (25 °C) above the transus. Measurements of the temporal evolution of the volume fraction of alpha were interpreted using numerical simulations based on the Whelan dissolution model modified to treat a distribution of particle sizes and the possible interaction of the concentration gradients developed around adjacent particles; i.e., soft impingement. The isothermal dissolution measurements were bounded by predictions from simulations with and without the soft-impingement assumption. Similar trends were found for continuous-heating behavior. In particular, slow or fast heating-rate observations were replicated by simulation predictions with or without the soft-impingement constraint, respectively.

Growth behavior of [formula omitted] coprecipitates in Ni-Base superalloys

Precipitation of the γ'' phase on {100} facets of preceding γ' precipitates is found to prevent the latter from overaging upon slow cooling from solution treatment in Ni-base superalloys based on the composition of alloy 718. By computer simulation using a multi-phase-field model, we find that the growth of a coprecipitate involves several concurrent and closely coupled processes, including thickening and lengthening of γ'' shells, growth of the γ' core along the 001γ', 011γ' and 111γ' directions, hard impingement between γ' and γ'' precipitates, and soft impingement among γ'' precipitates of different variants. These processes at different stages of growth are analyzed systematically as a function of coprecipitate size and configuration, and the results show that the growth kinetics of the γ' core in a coprecipitate is controlled by the interplay among: (1) partial removal of supersaturated γ matrix surrounding the γ' core by coprecipitation of γ'' shells, (2) cooperative growth of γ' and γ'' in the coprecipitates and (3) atomic mobility of γ'-formers in the γ'' phase. To maximize the effect of coprecipitation on preventing γ' from overaging upon slow cooling, the alloy composition and heat treatment schedule should be optimized to minimize the size of γ' cores at which coprecipitation of γ'' shells occurs and to reduce diffusion of γ'-formers through γ''.

Arthroscopic Technique for Iliopsoas Fractional Lengthening for Symptomatic Internal Snapping of the Hip, Iliopsoas Impingement Lesion, or Both

Pathology of the iliopsoas may cause painful internal snapping of the hip or labral damage from soft impingement. Favorable outcomes have been reported after arthroscopic release or fractional lengthening of the iliopsoas. In patients with risk factors for instability, restoration of other soft-tissue constraints such as the labrum and capsule should be performed if iliopsoas fractional lengthening is undertaken. The purpose of this article is to detail the step-by-step surgical technique of arthroscopic iliopsoas fractional lengthening, in addition to the indications, pearls, and pitfalls of the technique.