HIP Cycle Research Articles

Identification of the Mechanism Resulting in Regions of Degraded Toughness in A508 Grade 4N Manufactured Using Powder Metallurgy–Hot Isostatic Pressing

Powder metallurgy–hot isostatic pressing (PM-HIP) is a form of advanced manufacturing that offers the ability to produce near-net shape components that are otherwise not achievable via conventional forging or wrought manufacturing. Accessing the design space of PM-HIP is dependent upon the ability to achieve uniform or known properties in finalized components, which has resulted in a number of programs aimed at identifying properties achievable via PM-HIP manufacturing. One result of these programs has been the consistent observation of a variation in toughness observed for the low-alloy steel ASTM A508 Grades 3 and 4N. While observed, the degree of variability and the mechanism resulting in the variability have not yet been fully defined. Thus, a systematic approach to evaluate the variation observed in impact toughness in PM-HIP ASTM A508 Grade 4N was proposed to elucidate the responsible metallurgical mechanism. Four unique billets manufactured from two heats of powder with different particle size distributions (PSDs) were fabricated and tested for impact toughness and tensile properties. The degradation in impact toughness was confirmed to be location-specific where the near-can region of all billets had reduced impact toughness relative to the interior of each billet. The mechanism driving the location-specific property development was identified to be mobile oxygen that follows the thermal gradient that develops during the HIP cycle and leads to a redistribution of mobile oxygen where oxygen is concentrated ~1” inboard of the original canister/billet interface. Redistributed oxygen then forms stable oxides along coincident prior particle and prior austenite grain boundaries, effectively reducing the impact toughness. With the mechanism now addressed, necessary actions can be taken to mitigate the effect of the oxygen redistribution, allowing for use in PM-HIP A508 Grade 4N in commercial industry.

Effect of Post-Processing Treatment on Fatigue Performance of Ti6Al4V Alloy Manufactured by Laser Powder Bed Fusion

Fatigue properties of parts are of particular concern for safety-critical structures. It is well-known that discontinuities in shape or non-uniformities in materials are frequently a potential nucleus of fatigue failure. This is especially crucial for the Ti6Al4V alloy, which presents high susceptibility to the notch effect. This study investigates how post-processing treatments affect the mechanical performance of Ti6Al4V samples manufactured by laser powder bed fusion technology. All the fatigue samples were subjected to a HIP cycle and post-processed by machining and using combinations of alternative mechanical and electrochemical surface treatments. The relationship between surface properties such as roughness, topography and residual stresses with fatigue performance was assessed. Compressive residual stresses were introduced in all surface-treated samples, and after tribofinishing, roughness was reduced to 0.31 ± 0.10 µm, which was found to be the most critical factor. Fractures occurred on the surface as HIP removed critical internal defects. The irregularities found in the form of cavities or pits were stress concentrators that initiated cracks. It was concluded that machined surfaces presented a fatigue behavior comparable to wrought material, offering a fatigue limit superior to 450 MPa. Additionally, alternative surface treatments showed a fatigue behavior equivalent to the casting material.

Effects of the solution and first aging treatment applied to as-built and post-HIP CM247 produced via laser powder bed fusion (LPBF)

In this work CM247LC, a low weldable Ni-Based alloy, was produced using selective laser melting (SLM). Despite the initial process parameter optimization, the low defect volume fraction was still uncompliant with manufacturing standards. This condition is principally caused by the high γ’ volume fraction which strongly affects the alloy weldability. Nonetheless, a crack free condition was eventually achieved applying a γ’-sub-solvus Hot Isostatic Pressing Cycle (HIP) which lowered the defects fraction down to 0.04%. The HIP cycle also demonstrated to play an important role in the stabilization of the microstructure, considerably limiting the carbides coarsening during the following heat treatment. Apart from the effectiveness of the healing process brought by HIP, the material microstructure still needs an optimization process which will be described along this paper. In fact, the Initial microstructure obtained after the printing process (the as-built condition) as well as the one obtained after HIP (post-HIP) won’t meet the desired requirements. Namely, the dendritic and γ’ free microstructure of the as-built material or the one with coarse and disordered particles obtained right after HIP, still need a tailored homogenization process. This paper will show how the combined effect of the solution and first aging treatment will profoundly alter the γ’ precipitation. More specifically, here, a new heat treatment recipe was developed to promote the precipitation of ordered cuboidal primary γ’ so as to improve creep and high temperature fatigue resistance. Moreover, the use of a γ’ super-solvus temperature allowed to achieve a γ’ volume fraction as high as 73% reducing its average size to 520 nm. At the same time, such heat treatment caused a profound alteration of the crystalline structures of the material promoting a general grain coarsening and the formation of equiaxial grains.

Return to sports after hip resurfacing versus total hip arthroplasty: a mid-term case control study.

Hip resurfacing (HR) is an alternative to conventional total hip arthroplasty (THA) for the treatment of osteoarthritis (OA) in very active, young male patients. However, there is no study in the literature that has proven its benefits for high-impact sport over standard primary THA. The aim of the current study was to investigate the return to sport and function level of male patients after THA vs. HR. This prospective study is based on a telephone questionnaire for general health and sports activities. 40 HRs were matched with 40 THAs based on preoperative University of California Arthroplasty Score (UCLA), BMI, age at time of surgery and age at follow-up. The mean follow-up period was 56months (range 24-87months). HR patients showed a significantly higher High-activity arthroplasty score (HAAS) (14.9 vs. 12.9, p < 0.001) and Lower extremity activity scale (LEAS) (15.9 vs. 14.1, p < 0.001) and reached significantly higher values in the Hip cycle score (HCS) (44.7 vs. 35.7 p = 0.037) and Impact score (IS) (40.9 vs. 29.6, p < 0.002) than THA patients. No significant differences were found in the HOOS function section (91.4 vs. 90.3, p = 0.803) and the Pain numeric rating scale (NRS)-11 (0.6 vs. 0.9 p = 0.169). Patients with HR had a slightly higher Harris hip score (HHS) (97.8 vs. 95.6, p = 0.015) CONCLUSION: The current study suggests that young male patients are able to engage in higher activity levels after HR compared to standard THA.

Effects of physical activity on long-term survivorship after metal-on-metal hip resurfacing arthroplasty: is it safe to return to sports?

In previous studies, we identified multiple factors influencing the survivorship of hip resurfacing arthroplasties (HRAs), such as initial anatomical conditions and surgical technique. In addition, the University of California, Los Angeles (UCLA) activity score presents a ceiling effect, so a better quantification of activity is important to determine which activities may be advisable or detrimental to the recovered patient. We aimed to determine the effect of specific groups of sporting activities on the survivorship free of aseptic failure of a large series of HRA. A total of 661 patients (806 hips) representing 77% of a consecutive series of patients treated with metal-on-metal hybrid HRA answered a survey to determine the types and amounts of sporting activities they regularly participated in. There were 462 male patients (70%) and 199 female patients (30%). Their mean age at the time of surgery was 51.9 years (14 to 78). Their mean body mass index (BMI) was 26.5 kg/m2 (16.7 to 46.5). Activities were regrouped into 17 categories based on general analogies between these activities. Scores for typical frequency and duration of the sessions were used to quantify the patients' overall time spent engaging in sporting activities. Impact and cycle scores were computed. Multivariable models were used. We found no association between any category of activity and a decrease in survivorship. Impact and hip cycle scores also failed to show any association with revision for aseptic failure or wear. Return to sporting activities after surgery is safe for patients treated with well-designed and well-implanted HRA. Cite this article: Bone Joint J 2019;101-B:1186-1191.

Optimizing HIP and Printing Parameters for EBM Ti-6Al-4V

An investigation of HIP parameters for EBM Ti-6Al-4V has been performed with the aim to maximize the strength of the HIPed material. A lower HIP temperature of 800 °C and a higher pressure of 200 MPa gives the highest strength and is also enough to eliminate all internal defects. By printing material with intentionally induced porosity combined with an optimized HIP cycle the highest strength can be obtained.

Phase transformation under isostatic pressure in HIP

ABSTRACTThe new HIP cooling systems enable very fast cooling rates under isostatic pressure. This does not only enable shorter HIP cycles but also allows complete heat treatment cycles to be performed in one HIP cycle. It has been shown in previous studies that extreme pressures of several thousand bar can push phase transformation towards longer times. The new URQ HIP cooling systems give the opportunity to investigate the impact of pressures up to 2000 bar on phase transformation time dependency. For each of the two materials in this study, a comparison of austenite phase transformation time at 100 and 1700 bar was performed. The study was performed by isothermal heat treatment of specimens for a specific time followed by quenching. To evaluate the influence of pressure on hardenability, the phase fractions were evaluated using grid method on SEM images. The study found significant influence of HIP pressure on hardenability.

Investigation of Porosity Changes in Cast Ti6Al4V Rods After Hot Isostatic Pressing

The porosities of cast Ti6Al4V rods were investigated nondestructively using x-ray microcomputed tomography (microCT) before and after HIP. This allowed the visualization and quantification of porosity changes in the same samples, which indicate excellent pore closure for large pores. This is the first reported application of x-ray microCT for direct analysis of investment casting porosity before and after HIP. The method shows promise for further investigations using delayed HIP treatments or monitoring of pore closure at further varying HIP cycle settings. The nondestructive nature of the analysis has resulted in the interesting observation of small subsurface pores (<250 μm) unaffected by hot isostatic pressing in two of the samples.

The Relationship of Sporting Activity and Implant Survivorship After Hip Resurfacing

The effect of sports on the durability of the prosthesis after hip resurfacing has not been studied, to our knowledge. The purpose of this study was to correlate sporting activity levels calculated as Impact and Cycle Scores with the survivorship of the hip resurfacing implants. Four hundred and forty-five patients were surveyed from one to five years after surgery. The mean age of the patients was 48.7 years, and 74% were men. The Impact and Cycle Score included two scores: an Impact Score and a Hip Cycle Score. All patients were also evaluated with the University of California at Los Angeles activity score. Twenty-three patients (twenty-seven hips) underwent revision surgery after they had completed the survey. The mean duration of follow-up at the time of survey data collection was 1.9 years (range, 1.0 to 4.9 years), and the mean follow-up period was 10.2 years (range, 6.1 to 13.7 years). The mean Impact Score was 28.1 (range, 0 to 128), and the mean Hip Cycle Score was 33 (range, 0 to 144). Positive correlations were found between the University of California Los Angeles activity score and the Impact Score (r = 0.535) or Hip Cycle Score (r = 0.497). After adjustment for femoral component size, body mass index, and femoral defect size, a 10-point increment in Impact Score corresponded to a 37% increase (hazard ratio, 1.37; 95% confidence interval, 1.18 to 1.59) in the risk of revision arthroplasty, while a 10-point increment in the Hip Cycle Score increased the risk of revision by 22% (hazard ratio, 1.22; 95% confidence interval, 1.06 to 1.41).Patients with an Impact Score of < 50 had a risk of revision 3.8 times lower (hazard ratio, 3.8; 95% confidence interval, 1.6 to 8.9) than that of the patients with an Impact Score of ≥ 50, with a survivorship rate at eight years of 96.4% (95% confidence interval, 93.6% to 98.0%) compared with 88.8% (95% confidence interval, 74.7% to 95.3%). We found no association between the University of California at Los Angeles activity score and the survivorship of the implants. High levels of sporting activities can be detrimental to the long-term success of hip resurfacing devices, independently from other risk factors. Patients seeking hip resurfacing are usually young and should limit their involvement in sports to levels that the implant construct will be able to tolerate.

Loss and Recovery of Transparency in Pressure‐Consolidated Lu3Al5O12

Pr‐doped Lu3Al5O12 (LuAG) transparent ceramic, a potential scintillator material, was fabricated by sinter/hot isostatic pressing (HIP). The specimens were subjected to various post‐densification heat treatments and the evolution of porosity and its relationship to transparency was monitored and studied. Annealing was necessary to remove discoloration and to restore stoichiometry, but when performed at too high a temperature it caused a severe decrease in transparency. Transparency was restored by reHIPing, indicating that some nanometer‐size pores remained even after the original HIP cycle, which expanded in size during annealing and contracted again during re‐HIPing. Annealing at a lower temperature restored stoichiometry without serious transparency degradation, due to a favorable difference in diffusion rates for mass transfer and O2− diffusion. This phenomenon illustrates a fundamental difference between residual porosity in ceramics consolidated by pressureless and pressure‐assisted processes.

Effect of HIP temperature on microstructure and low cycle fatigue strength of CuCrZr alloy

In order to investigate the effect of the HIP cycle temperatures on the metallurgic degradation and the mechanical properties of CuCrZr alloy, assessments of the microstructure, tensile test, Charpy impact test and low cycle fatigue test are performed for various heat treated CuCrZr alloys, which were solution-annealed followed by water-quenched and aged state of CuCrZr with simulated HIP cycle at temperatures of 980 and 1045°C. Grain growth occurred on 1045°C HIP CuCrZr, though slightly on 980°C HIP CuCrZr. Metallurgic degradation such as voids was not found by optical and SEM observations. There were coarse precipitates in all the CuCrZr and the precipitates did not easily dissolve at 980°C. The low cycle fatigue strength of 1045°C HIP CuCrZr was lower than that of other CuCrZr because of the metallurgic degradation caused by the heat cycle, while that of other CuCrZr was corresponding to the best fit curve of ITER MPH.

Manufacture of a shield prototype for primary wall modules

In the frame of the blanket module (BM) development for ITER, an R&D programme was implemented for the manufacture of a shield prototype by powder hot isostatic pressing (HIPping). The manufactured shield is a full-scale module No. 11a. Starting from a forged block of 1350 mm × 1300 mm × 450 mm, the main machining steps as deep drilling (1200 mm), 3D machining and sawing were performed. Tubes were 3D bent and large number of small parts were designed and machined. By welding together all the sub-parts we erected the main part of the water coolant circuit. Once the water circuit was built; the shield was completed using powder HIPping together with forged block embedding the tubes in a final solid part. The powder/solid HIP is used to minimize the number of BM seal welds in front of plasma. It increases the reliability of the components during operation. About 300 kg of stainless steel powder was densified together with the forged block. 3D measurement was done before and after the HIP cycle to collect the data to be compared with theoretical model. It allows to predict the main distortions of the solid bulk. Ultrasonic examination of the densified powder on the stainless steel bulk and around the bended tubes was performed as well as mechanical characterization of the samples. The recess for stub key attachment on the vacuum vessel side, the hydraulic connector, the key for the primary wall panel attachment on the front side and the link between the four parallel water coolant circuits were then machined to achieve the shield prototype.

High performance and high complexity net shape parts for gas turbines: the ISOPREC® powder metallurgy process

ISOPREC® is a powder metallurgy process in which a highly sophisticated mould is filled with powder and further densified through a HIP cycle. After compaction, the mould is mechanically or chemically removed, and a net shape part is obtained. Examples of applications of this technology to Inconel 625, Ti-6-4 and A316LN are presented. High dimensional accuracy and mechanical performance are obtained for complex parts, therefore minimizing cost and production cycle time for such high level components.

Scratch-swim hybrids in the spinal turtle: blending of rostral scratch and forward swim.

Turtles with a complete transection of the spinal cord just posterior to the forelimb enlargement at the D2-D3 segmental border produced coordinated rhythmic hindlimb movements. Ipsilateral stimulation of cutaneous afferents in the midbody shell bridge evoked a rostral scratch. Electrical stimulation of the contralateral dorsolateral funiculus (DLF) at the anterior cut face of the D3 segment activated a forward swim. Simultaneous stimulation of the ipsilateral shell bridge and the contralateral DLF elicited a scratch-swim hybrid: a behavior that blended features of both rostral scratch and forward swim into each cycle of rhythmic movement. This is the first demonstration of a scratch-locomotion hybrid in a spinal vertebrate. The rostral scratch and the forward swim shared some characteristics: alternating hip flexion and extension, similar timing of knee extensor activity within the hip cycle, and a behavioral event during which force was exerted against a substrate. During each cycle, each behavior exhibited three sequential stages, preevent, event, and postevent. The rostral scratch event was a rub of the foot against the stimulated shell site. The forward swim event was a powerstroke, a hip extension movement with the foot held in a vertical position with toes and webbing spread. The two behaviors differed with respect to several features: amount of hip flexion and extension, electromyogram (EMG) amplitudes, and EMG duty cycles. Scratch-swim hybrids displayed two events, the scratch rub and the swim powerstroke, within each cycle. Hybrid hip flexion excursion, knee extensor EMGs, and hip flexor EMGs were similar to those of the scratch; hybrid hip extension excursion and hip extensor EMGs were similar to those of the swim. The hybrid also had three sequential stages during each cycle: 1) a combined scratch prerub and swim postpowerstroke, 2) a scratch rub that also served as a swim prepowerstroke, and 3) a swim powerstroke that also served as a scratch postrub. Merging of the rostral scratch with the forward swim was possible because of similarities between the sequential stages of the two forms, making them biomechanically compatible for hybrid formation. Kinematic and myographic similarities between the rostral scratch and the forward swim support the hypothesis that the two behaviors share common neural circuitry. The common features of the sequential stages of each behavior and the production of scratch-swim hybrids provide additional support for the hypothesis of a shared core of spinal cord neurons common to both rostral scratch and forward swim.

Electrically evoked fictive swimming in the low-spinal immobilized turtle.

Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the contralateral dorsolateral funiculus (cDLF) at the level of the third postcervical segment (D(3)). Fictive hindlimb motor output was recorded as electroneurograms (ENGs) from up to five peripheral nerves on the right side, including three knee extensors (KE; iliotibialis [IT]-KE, ambiens [AM]-KE, and femorotibialis [FT]-KE), a hip flexor (HF), and a hip extensor (HE). Quantitative analyses of burst amplitude, duty cycle and phase were used to demonstrate the close similarity of these cDLF-evoked fictive motor patterns with previous myographic recordings obtained from the corresponding hindlimb muscles during actual swimming. Fictive rostral scratching was elicited in the same animals by cutaneous stimulation of the shell bridge, anterior to the hindlimb. Fictive swim and rostral scratch motor patterns displayed similar phasing in hip and knee motor pools but differed in the relative amplitudes and durations of ENG bursts. Both motor patterns exhibited alternating HF and HE discharge, with monoarticular knee extensor (FT-KE) discharge during the late HF phase. The two motor patterns differed principally in the relative amplitudes and durations of HF and HE bursts. Swim cycles were dominated by large-amplitude, long-duration HE bursts, whereas rostral scratch cycles were dominated by large-amplitude, long-duration HF discharge. Small but significant differences were also observed during the two behaviors in the onset phase of biarticular knee extensor bursts (IT-KE and AM-KE) within each hip cycle. Finally, interactions between swim and scratch motor networks were investigated. Brief activation of the rostral scratch during an ongoing fictive swim episode could insert one or more scratch cycles into the swim motor pattern and permanently reset the burst rhythm. Similarly, brief swim stimulation could interrupt and reset an ongoing fictive rostral scratch. This shows that there are strong central interactions between swim and scratch neural networks and suggests that they may share key neural elements.

Macroblock manufacturing by ‘hip assisted brazing’ method

The aim of this work was to demonstrate the potential of an original technology which allows the manufacturing of large size so-called carbon fibre composite ‘macroblock’ tube-in-tile components associated with a reliability for a future industrial production. This process includes the combinations of two techniques: (a) a hot isostatic pressing cycle to allow intimate contact of a copper tube with a CFC block during all the process; (b) a brazing operation during the HIP cycle to perform a good joint between both substrates. Finally, two prototypes have been realized and a non destructive evaluation of the quality of the joint has been carried out.

Microstructure and mechanical properties of a PM TiAl-W alloy processed by hot isostatic pressing

A PM Ti-48at.%Al-2at.%W alloy was fully consolidated under two HIp conditions. A HIP cycle with a peak temperature of 1360 °C produced a fine-grained duplex microstructure. Increasing the peak temperature to 1395 °C developed a coarse-grained fully lamellar microstructure. The former yielded better room-temperature tensile strength and ductility, while the latter showed slightly higher ultimate tensile strength at 850 °C and superior creep resistance at 760 °C, 276 MPa. The fracture surfaces and deformation substructures of the tested specimens were analyzed and correlated with their mechanical behaviour. The effect of HIP conditions on the microstructures and the microstructure-property relationships is discussed.

Mechanical entrainment of fictive locomotion in the decerebrate cat

1. We examined the ability of muscular and joint afferents from the hip region to entrain fictive locomotion evoked by stimulation of the mesencephalic locomotor region in the decerebrate cat by mechanically imposed, sinusoidal hip flexion and extension movements. 2. A method is presented for qualitative and quantitative analysis of entrainment. 3. Hip joint capsular afferents were shown by denervation experiments to be unnecessary for mediating locomotor entrainment. 4. As the population of muscular afferents was progressively decreased by selective denervation, the strength of entrainment concomitantly decreased, even though a few as two small intrinsic hip muscles were still effective in producing entrainment. The ability to entrain locomotion was abolished with complete ipsilateral denervation. 5. Entrainment was observed with low amplitude hip angular displacement of 5-20 degrees, which would be expected to activate low-threshold, stretch-sensitive muscle afferents. 6. The extensor burst activity occurred during the period of imposed hip flexion, which corresponded to passive stretching and loading of the extensor muscles, while the flexor burst activity occurred during the latter portion of the imposed hip extension, which corresponded to passive stretching of the flexor muscles (when attached) and release of the extensors. During harmonic entrainment, the match of hip cycle duration and step cycle duration was accomplished by a variation in extensor electroneurogram (ENG) burst duration. These results are consistent with a positive feedback mechanism where low-threshold afferent activity from the extensor musculature is used by the rhythm generator to prolong the extension phase of locomotion. 7. A hip cycle frequency-dependent phase shift of ENG activity was observed. This may indicate that the locomotor rhythm generator is dependent on more than just static positional or threshold load information for modulation of the step cycle frequency and switching between flexion and extension phases. 8. Subharmonic forms of entrainment were observed when the number of innervated muscles was markedly reduced. The occurrence of subharmonic entrainment characterizes the locomotor rhythm generator as a nonlinear oscillator. 9. To modulate the stepping frequency, the afferent pathways responsible for entrainment must be directly connected to the neural circuitry responsible for rhythm generation. The rhythm generating interneurons must receive a high degree of convergence from afferents arising from a variety of muscles spanning the hip joint.

Densification behaviour of a PM titanium alloy during HIP

Knowledge of the time dependent densification behaviour of technical powder materials during HIP procedure is of interest not only to understand the fundamental mechanisms taking place, but also to govern all stages of the HIP cycle, allowing cost effective production of materials with homogeneous and reproducible mechanical properties.

Bimetallic Coatings for Twin - Screw Extruder Barrels

ABSTRACTIn this paper the development of novel wear/corrosion resistant coatings for twin screw extruders used in the food industry is discussed. The conventional materials used for extruder applications are reviewed and their limitations highlighted. The requirements for a new surface engineering philosophy are introduced and utilised to develop a new manufacturing system for the coating of extruder barrels. These coatings are based on Ni/Cr/B/Si/Fe alloys containing WC particulate. The processing route combines conventional PM technology with consolidation of the coating by hot isostatic pressing (HIPping). The HIP cycle is tailored to optimise the coating/substrate adhesion and the coating microstructure. Examples are given which illustrate the superior performance of these HIPped bimetallic coatings compared to conventional surface treatments.