The goal of the quench and partition (Q&P) process for steel heat treatment is to enrich austenite with carbon during a partitioning treatment after initial quenching below the martensite start ...temperature (Ms). Two proposed mechanisms for austenite carbon enrichment during partitioning include carbon transport from martensite and/or the formation of carbide-free bainite. Theoretical calculations show experimentally measured austenite fractions are difficult to explain based upon a mechanism involving solely bainite formation. Carbon partitioning from martensite provides a more satisfactory explanation, although the formation of bainite during partitioning cannot be completely excluded.
Restoration of the extensor apparatus in the case of advanced tendon defects as part of revision total knee arthroplasty (TKA). Reconstruction and augmentation using vascularized gastrocnemius muscle ...and tendon.
Advanced degeneration of the extensor apparatus (patella tendon; quadriceps tendon) with or without discontinuity, following revision arthroplasty.
Persistent infection or pending TKA revision. Damaged gastrocnemius or soleus muscle or Achilles tendon.
Extension of the surgical TKA-access medial-distally. Separation of the medial gastrocnemius muscle along the raphe and preparation of the distal tendon from the soleus portion. Transposition into the defect site, augmentation or reconstruction of the defect by double turn of the gastrocnemius tendon. The muscle belly serves to adequately cover the tendon as well as the ventral knee joint. Mesh coverage of the muscle.
Immobilization of the knee and ankle for 10 days until mesh graft healing. Stepwise increasing flection of the knee with 30°/60°/90° every 2 weeks. Total weight bearing with secured full extended knee, no weight bearing with flexed knee for 6 weeks.
In 9 patients, 3 with complete rupture of the patellar tendon, 5 with destruction of the extensor apparatus, and 1 patient with rupture of the quadriceps tendon following TKA revision, good functional results were achieved with active extension of the knee joint and standing/gait stability 6 months after surgery.
It is usually assumed that ferrous pearlite can form only when the average austenite carbon concentration
C
0
lies between the extrapolated Ae3 (
γ
/
α
) and Acm (
γ
/
θ
) phase boundaries (the ...“Hultgren extrapolation”). This “mutual supersaturation” criterion for cooperative lamellar nucleation and growth is critically examined from a historical perspective and in light of recent experiments on coarse-grained hypoeutectoid steels which show pearlite formation outside the Hultgren extrapolation. This criterion, at least as interpreted in terms of the average austenite composition, is shown to be unnecessarily restrictive. The carbon fluxes evaluated from Brandt’s solution are sufficient to allow pearlite
growth
both inside and outside the Hultgren Extrapolation. As for the feasibility of the
nucleation
events leading to pearlite, the only criterion is that there are some
local
regions of austenite inside the Hultgren Extrapolation, even if the
average
austenite composition is outside.
Various underlying diseases can lead to a pointed foot in children and adults. If the gastrocnemius and soleus muscles are structurally shortened, various surgical procedures are available to correct ...this malposition. A preferred method for restoring a normal dorsiflexion of the upper ankle joint is percutaneous achillotentomy according to Hoke. Consideration of the physiological-anatomical torsion of the Achilles tendon as it corresponds to the White technique and is recommended by some authors shows in our experience no advantages. In the present work, we show a modified, likewise minimally invasive form of this surgical method with which immediate full weight-bearing of the affected lower extremity is possible from postoperative day 1.
All clinically relevant structural pointed foot, for primary and/or for revision treatment.
Infection in the area of the operation.
No tourniquet, 3 incisions with the 15 mm knife: (1) medial distal at the transition from the Achilles tendon to the calcaneus, (2) medial proximal approximately 7 cm proximal to the 1st stab incision, (3) lateral, midway between the first two incisions; no skin suturing, application of a lower leg cast.
On postoperative day 1, cast hybridization using Scotchcast (3M Deutschland GmbH, Neuss, Germany), followed by pain-adapted full weight-bearing; removal of the cast in the outpatient department after 4 weeks.
A total of 104 patients underwent surgery, 1 case of a local pressure point, no infections, no overcorrections, no Achilles tendon ruptures, in one case a postoperative relapse due to a broken cast. The risk of overcorrection to the foot, which was considered the main complication in the literature, did not occur in any of the cases.
The isothermal growth of partitioned pearlite in a series of high purity Fe–C–Mn alloys over the temperature range 575–650 °C has been investigated. Two types of behavior were observed. For those ...alloys transformed within the (α+M
3C) two phase field of the respective Fe–C–Mn isothermal section, growth occurred under steady-state conditions, with constant rate and interlamellar spacing. Those compositions transformed within the (γ+α+M
3C) three phase field invariably transformed under non-steady-state conditions with a growth rate which decreased and an interlamellar spacing that increased (divergent) in time. Detailed analytical transmission electron microscropy (ATEM) measurements of the Mn concentration profiles across the γ/α and γ/M
3C growth interfaces were made as a function of time for two alloys transformed at 625 °C. For the alloy transformed within the (α+M
3C) two phase field, the Mn contents inherited by the growing α and M
3C were remarkably constant for much of the reaction and are well approximated by the local equilibrium values. In the case of the alloy transformed within the (γ+α+M
3C) three phase field, the Mn contents inherited by the growing α and M
3C both increased with time. The Mn contents of the growing M
3C were at all times observed to fall within the bounds expected by the local equilibrium (LE) model, whereas a Mn enrichment over and above the LE values was observed for the growing ferrite. The effect of this enrichment on the expected pearlite growth rate is shown to be very small and it is concluded that the LE approximation for the interfacial conditions during pearlite growth under the conditions studied is a good approximation.
Detailed examinations of shape memory effect (SME) deformation structures in martensite of U–14
at.% Nb were performed with electron backscatter diffraction (EBSD) and transmission electron ...microscopy (TEM). An accommodation strain analysis, which has been previously used to predict SME deformation structures and texture evolution in polycrystalline material, was also performed. Martensite variants and twin relationships observed with EBSD after compressive or tensile deformation were determined to be consistent with those expected from calculated accommodation strains. Focused ion beam (FIB) was used to select twinned regions identified with EBSD for more detailed TEM analysis to verify the presence of these specific twins. The observed SME twinning systems in the martensite agree with previous TEM observations and the predicted
{
1
¯
76
}
twinning system was observed experimentally for the first time in U–14
at.% Nb using these complementary techniques.
Low temperature aging (<350
°C) of U–13
at.% Nb martensite results in increased strength levels accompanied by significant ductility loss. To determine the decomposition mechanism(s) responsible for ...these mechanical property changes, atom probe tomography was used to examine the niobium and impurity distributions after aging at 200 or 300
°C for times ranging from 2
h to 70
days. No patterns of niobium or impurity atoms were observed that would indicate segregation to the martensitic twin interfaces, making this hardening mechanism unlikely. Phase separation into roughly equiaxed regions of high and low niobium concentration was clearly observed after aging at 300
°C for 70
days. However, only subtle niobium concentration changes were observed after aging at 200
°C relative to the as-quenched condition, indicating that conventional phase separation is an unlikely explanation for the dramatic mechanical property changes at 200
°C. Therefore, consideration of aging mechanisms other than segregation and phase separation may be warranted.
Complicating factors that have stymied understanding of uranium-niobium’s aging response are briefly reviewed, including (1) niobium inhomogeneity, (2) machining damage effects on tensile properties, ...(3) early-time transients of ductility increase, and (4) the variety of phase transformations. A simple Logistic-Arrhenius model was applied to predict yield and ultimate tensile strengths and tensile elongation of U-4Nb as a function of thermal age. Fits to each model yielded an apparent activation energy that was compared with phase transformation mechanisms.
X-ray diffraction analyses of aged U–Nb alloys Volz, H.M.; Hackenberg, R.E.; Kelly, A.M. ...
Journal of alloys and compounds,
10/2007, Letnik:
444
Journal Article, Conference Proceeding
Recenzirano
An aging study of compositionally homogeneous U–5.6Nb and U–7.7Nb (wt.%) was undertaken to improve the understanding of the decomposition of metastable martensitic phases in the U–Nb system. ...Artificially aging these depleted (
238U) uranium alloys at 373, 473, 523 and 573
K for times up to 70 days resulted in significant age hardening. However, the microstructural changes giving rise to this hardening are subtle and elude standard light optical and electron microscopy techniques; this subtlety motivated the present study of aging-related changes by X-ray diffraction. A sealed tube X-ray diffractometer was used to record powder diffraction patterns from these aged polycrystalline U–Nb samples along with a CeO
2 standard. Data were analyzed using GSAS for full-pattern Rietveld refinements. Planar defects as well as strain broadening appear to have caused unusual peak profiles, which makes data interpretation challenging. Lattice parameter and unit cell volume trends are presented. U–5.6Nb experienced a reversal in the
b lattice parameter and unit cell volume during aging, which has both similarities and differences to aging in dilute U–Ti and U–Mo alloys. The longest-time aging unit cell volume trends of U–5.6Nb indicate Nb depletion of the matrix phase, while the corresponding behavior at all aging times in U–7.7Nb is indicative of Nb enrichment in its matrix phase.
Induction heating has permitted great progress in the surface hardening of a wide variety of steels, but results in a wide range of local thermal cycles. The metallurgical changes during rapid ...heating and cooling have not been sufficiently studied with respect to heating rate and prior microstructure. In the present investigation, induction dilatometry was performed on 5150 steel with ferrite-pearlite and tempered martensite initial microstructures to assess effects of experimentally controlled prior microstructure and heating rate on austenitization kinetics. Heating rates were varied from 0.3 to 300 °C/s to simulate industrial processes, and post-hardening metallography and hardness testing were performed. Results show that the transformation kinetics for prior ferrite-pearlite microstructures are significantly slower than for prior tempered martensite microstructures, although hardness is equivalent for a given thermal cycle. Metallographic evidence suggests significant remnant segregation of chromium in regions of pearlitic cementite (enriched); evidence of segregation was not observed metallographically for prior tempered martensite. Diffusion-based transformation simulations support observed ferrite-pearlite alloy segregation, suggest residual alloy segregation is possible for prior tempered martensite, and can be used to tailor austenitization thermal cycles to process requirements. Detailed time and temperature-dependent local microstructure development results from this study are directly applicable to practical induction hardening simulations.
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