Aging Treatment Research Articles

Effect of Precipitation Heat Treatment on a Mechanically Alloyed Al‐Based Composite Reinforced with Metallic Glassy Powder

An Al‐based composite reinforced with titanium‐based metallic glassy particles is synthesized by the powder metallurgy method through mechanical alloying followed by hot extrusion. The effect of precipitation heat treatment on the structure and properties of the composite is studied. During aging of the solution‐treated composite, crystallization of the metallic glassy reinforcement becomes more pronounced as the solutionizing temperature, solutionizing time, aging temperature, and aging time increase. A reaction layer has formed at the interface between the reinforcement and the matrix after the aging treatment. It is found that the addition of metallic glassy particles promotes precipitation of the nanophase in the matrix. With appropriate heat treatment, the compressive strength, yield strength, and fracture strain of the composite have increased to 942, 635 MPa, and 27%, respectively. Herein, it is demonstrated that the mechanical properties of these composites can be further enhanced through an appropriate heat treatment process, thereby having significant potential for a variety of industries, including aerospace, automotive, and defense, where high‐strength, lightweight materials are critical for performance and safety.

OGC SO32 - Propensity score analysis of the impact of deprivation and the COVID-19 pandemic on Upper Gastro Intestinal (UGI) cancer surgery outcomes

Abstract Background Deprivation is a complex, multifaceted concept, not synonymous with poverty, but with the potential to widen health inequalities. This study aimed to explore demographic disparities in patients undergoing UGI cancer surgery in a UK regional cancer network during the COVID-19 pandemic. Method Consecutive 881 patients were studied prospectively (median age 67 (24 - 89) yr., 703 m, 178 f; 518 oesophageal, 363 gastric; 837 Adeno-, 44 SCC) over 13 years. The COVID-19 pandemic was defined as the 24-month period from February 1, 2020 to January 31, 2022, during which 118 patients were treated. The demographic profile of the pandemic cohort was compared with that of the 763 patients treated outside this period incorporating a propensity score analysis. Primary outcomes were operative morbidity, mortality, and one-year survival. Wales’ Index of Multiple Deprivation was used to assess deprivation disparity. Results A 24% reduction in the number of cancer operations was observed during the first pandemic year. No difference was observed in age, gender, histology, tumour site, ASA grade, or oncological treatment. During COVID-19 the proportion of patients from the two most deprived quartiles receiving potentially curative surgery fell from 53.2% to 40.7% (p=0.012). No difference was observed in severe morbidity (Clavien-Dindo >3, 22.2% vs. 19.8%, p=0.897), 30-day mortality (2.5% vs. 2.4%, p=0.886), or one-year survival (82.4% vs. 78.8%, p=0.374). Conclusion UGI cancer surgery safely continued during COVID-19, but patients from areas of high deprivation were over 20% less likely to access curative surgical treatment compared with before and after COVID-19. This emphasises the need for bespoke strategies to mitigate the disproportionate impact of any future pandemic on patients living in deprived geographical areas.

Effect of Aging Temperature on the Mechanical Properties, Biodegradability, and Cytocompatibility of the as‐Rolled Zn‐3Al‐1Cu Alloy

The inherent low strength of zinc (Zn) alloys limits their application, and aging treatment is a method that can be used to improve the properties of Zn alloys significantly. In this work, the effects of aging temperature on microstructure, mechanical properties, and corrosion resistance of the as‐rolled Zn‐3Al‐1Cu alloy are studied. The results show that the mechanical properties and corrosion resistance of the alloy can be significantly improved by tuning the aging temperature. Through aging treatment, the grain size of the second phase grows and more of the second phase is precipitated, which improves the mechanical properties and plasticity of the as‐rolled Zn‐3Al‐1Cu alloy. The tensile and yield strengths of the as‐rolled Zn‐3Al‐1Cu alloy aged at 80 °C are the highest, which are 206.11 ± 1.63 and 177.57 ± 1.70 MPa, respectively. Conversely, the alloy aged at 160 °C displays the best plasticity, where its elongation reaches 25.66 ± 0.49%. In addition, aging at 160 °C leads to the best corrosion resistance, reaching a corrosion rate obtained by the electrochemical test of 0.0016 mm year−1.

Abstract 4147633: Structural and Electrophysiological Cardiac Changes in Children with Osteogenesis Imperfecta (OI)

Introduction: Osteogenesis imperfecta (OI) is an inherited type 1 collagen disorder leading to bone fragility and increased fractures. Cardiovascular disease is the leading cause of death of adults with OI, but studies on cardiac changes from this collagen defect in children are sparse. We aim to fill this gap by assessing changes in EKG and echocardiogram (ECHO) variables in children with OI. Hypothesis: Children with OI will exhibit arrhythmogenic EKG changes and/or ECHO abnormalities which will precede changes that are documented in adults. Methods: 53 children with OI receiving care at Children’s Mercy-Kansas City were identified via ICD-10 codes. 64 with Duchenne Muscular Dystrophy (DMD, expected cardiac abnormalities) and 55 with non-accidental trauma (NAT, no expected cardiac abnormalities) served as controls. We specifically compared the most recent EKG and ECHO metrics extracted from medical charts by Kruskal-Wallis testing. Results: EKG: Children with OI differed from both NAT and DMD. OI had shorter median PR intervals (p<0.001) plus longer median QRS (p<0.001) and QTc intervals (p=0.002) than NAT. DMD had the shortest PR and longest QRS and QTc (see Table). Echo: The three groups showed no difference in systolic/diastolic BP or LV thickness. However, OI differed from NAT and/or DMD in other metrics. OI had higher end diastolic volume (p<0.001), end systolic volume (p<0.001) and stroke volume (p<0.05) than NAT, but lower values than the DMD group. Similarly, OI children had higher LV mass and LV internal diastolic and systolic diameters than NAT, but lower than DMD (p<0.001). OI LVOT diameter and Aortic root diameter were lower than NAT, but not as low as DMD (p<0.05 and p<0.001, respectively). Conclusion: Children with OI exhibit EKG and ECHO abnormalities that are similar to but less severe than for DMD, a group in which cardiovascular abnormalities are well documented. These abnormalities may be predictive of arrythmia/sudden cardiac death and/or functional decline in heart function. Our data suggest that OI children could benefit from ongoing routine cardiology studies along with orthopedic/metabolic management. Future studies would assess effects of age and OI treatments on cardiac abnormalities.

Durvalumab Following Chemoradiotherapy for Stage III Non-small Cell Lung Cancer: Differences in Survival Based on Age and Post-Progression Systemic Therapy.

Concurrent chemoradiotherapy (cCRT) followed by 1 year of the immune checkpoint inhibitor (ICI) durvalumab is standard of care for patients with unresectable stage III nonsmall cell lung cancer (NSCLC). The purpose of this study was to evaluate survival outcomes of (1) cCRT followed by durvalumab in patients older versus younger than 75 years of age and (2) post-progression treatment with ICI alone versus chemotherapy alone versus combined ICI and chemotherapy. Patients with unresectable stage III NSCLC treated between January 2018 and July 2023 with cCRT followed by durvalumab were identified retrospectively. Progression-free survival (PFS) and overall survival (OS) from ICI start were analyzed in three cohorts aged < 65, 65-74, and ≥ 75 years. Multivariable Cox proportional hazard regression modelling of factors associated with OS was undertaken. Logistic regression analysis identified risk factors of early durvalumab discontinuation for toxicity. Time from first salvage drug treatment to death (OS-2) was described. A total of 472 patients were analyzed: the proportions aged < 65, 65-74, and ≥ 75 years were 34.3%, 42.8%, and 22.9%, respectively. Odds of early durvalumab discontinuation was 2.2-fold greater in the oldest (versus youngest) cohort. Age associated differences in median PFS (26.7months, 20.3months, and 14.2months; p< 0.001) and OS (60.8months, 44.4 months, and 27.6 months; p< 0.001) were observed. On multivariable analysis, factors associated with shorter OS were age ≥ 75years (versus < 65), performance status 2/3 (versus 0/1), stage IIIC (versus IIIA), neutrophil to lymphocyte ratio (per 7.43 unit increase), Charlson comorbidity index (per 1 unit increase), tumoral PD-L1 expression < 1% (versus ≥ 50%, 1-49%, or unknown), and squamous histology (versus non-squamous). Of 264 patients with disease progression, 48.5% received subsequent drug therapy. Median OS-2 was longer with ICI alone (9.9 months) or ICI-chemotherapy (11.8 months) than platinum doublet chemotherapy (6.7 months.) For recurrences < 6 months from the last durvalumab infusion, OS-2 were similar across treatment groups. In the studied cohort, OS was significantly shorter for patients ≥ 75 years of age treated with cCRT followed by durvalumab compared to those < 65 years. Post-progression systemic therapy was associated with modest efficacy, underscoring the need for new therapies.

Microstructural evolution, phase transformation, and mechanical properties of Corrax-Ta40Nb60C-VC composite using vacuum sintering, solid-solution, sub-zero, and aging treatments

Microstructural evolution, phase transformation, and mechanical properties of Corrax-Ta40Nb60C-VC composite using vacuum sintering, solid-solution, sub-zero, and aging treatments

Effect of heat treatment on microstructure and mechanical properties of WE43 alloy fabricated by wire arc additive manufacturing

Heat treatment is an effective method to improve the mechanical properties of Wire Arc Additive Manufacturing (WAAM) WE43 alloy. This study investigates the effects of heat treatment on the microstructure and mechanical properties of the WE43 alloy processed by WAAM. The as-deposited samples exhibit a uniform equiaxed crystal structure, with grain size gradually increasing as the number of deposited layers grows. The as-deposited microstructure comprises eutectics and a small amount of cubic phases, and the phase content escalates as the amount of deposited layers increases, influenced by the cumulative effect of multiple thermal cycles. At lower solid solution temperatures (480 ℃ × 8h), most of the eutectic phase remains undissolved. During tensile testing, undissolved eutectics tend to cause stress concentrations, leading to cracks that result in sample fractures, negatively affecting the mechanical properties. At higher solid solution temperatures (520 ℃ × 8h), most of the eutectic dissolves, but abnormal grain coarsening (AGC) in the interlayer fine-grain region occurs, causing a significant reduction in the sample's mechanical properties. After solid solution treatment at 500 °C for 8hours, only a small amount of eutectics remains undissolved, and the AGC phenomenon is not observed, resulting in an optimal solid solution effect. Subsequently, after aging treatment at 225 °C for 18hours, dense nanoscale β′′ phases precipitated within the alloy grains, significantly improving the mechanical properties. The samples achieved optimal performance, with UTS, YS, and EL of 323±15.2MPa, 225±11.3MPa, and 8.4±1.1%, respectively.

Investigation on effect of L12 and B2 phases on tensile properties and mechanisms of Al0.3CoCrFeNi high entropy alloy through aging treatment

Al0.3CoCrFeNi high entropy alloys (HEAs) have excellent mechanical properties due to the large tunability of microstructures, which makes them one of the most promising candidates for engineering application. In the aspect of enhancing tensile properties, precipitation strengthening was verified effective in this HEA and more studies are needed to deepen relative understanding. In this work, Al0.3CoCrFeNi HEAs with coarse-grained single FCC (A) and fine-grained triplex FCC + B2 + σ (B) structures were aged at different temperatures and times to precipitate second phases, and the tensile properties and mechanisms of aged specimens were studied. The results showed that aging of A resulted in the main precipitation of L12 phases throughout FCC matrix and increasing aging temperature obviously increased L12 size, whereas increasing annealing time had minor effect on phase coarsening. At small L12 size of ~2.0nm, stacking fault shearing mechanism was activated during tension and planar dislocation configurations were formed, leading to simultaneous increase of strength and ductility. With increasing L12 size to ~10.0nm, the deformation mechanism was transformed into anti-phase boundary shearing and Orowan bypassing and wavy dislocation configurations predominated, which resulted in the significant increase of yield strength from ~263MPa to ~433MPa without sacrificing notable ductility. On the other hand, aging of B induced the formation of fine B2 phases at residual dislocations and enhancement of tensile yield strength from ~705MPa to ~759MPa. The ductility decreased slightly from ~32% to ~28%, which was related to the plastic deformation of B2 phases. However, it was found that the tensile strengths could not be continuously increased by further increasing aging temperature or time. These findings provide insights into the development of precipitation strengthened HEAs with good mechanical properties.

Increasing the high-temperature mechanical properties of Mg-Gd-Y-Zn alloys by adding AlN/Al particles

The AlN particles reinforced Mg-10Gd-3Y-1Zn (GWZ) composites were prepared by mixing AlN/Al particles using ball milling followed by stirring casting method. The influence of AlN/Al particles on the microstructural evolution and high-temperature mechanical properties of GWZ alloys were revealed and discussed. With AlN/Al particles added into the as-cast alloys, the Mg3RE phase was transformed into lamellar LPSO phase, while the content of Al2RE and LPSO phase increased. Since the Al2RE and AlN were effective nucleation sites for α-Mg, the grain size of AlN/Al-GWZ composites was reduced obviously from 126.1 to 39.8 μm. After homogenization, due to the coherent lattice matching relationships between 18R-LPSO phase and Al2RE or AlN particles, the 18R-LPSO phase nucleated on the Al2RE and AlN particles. After ageing treatment, the 2AlN/Al-GWZ composite showed the optimum mechanical properties at 250 °C, with the yield strength, ultimate tensile strength and elongation of 247.1 MPa, 265.5 MPa and 4.0%, respectively. The strengthening effect was primarily originated from the AlN particles, Al2RE and LPSO phases in the 2AlN/Al-GWZ composite. Besides, the composites can achieve the enhancement of high-temperature strength without the sacrifice of plasticity due to the coordinated deformation of AlN particles as well as the refinement of grains.

Local element segregation-induced cellular structures and dominant dislocation planar slip enable exceptional strength-ductility synergy in an additively-manufactured CoNiV multicomponent alloy with ageing treatment

We proposed an additively manufactured equiatomic CoNiV multicomponent alloy (MCA) using a conventional laser powder bed fusion (LPBF) method, and an exceptional strength-ductility synergy of the alloy was attained through a simple post-ageing treatment. Pronounced hierarchical microstructures were achieved in our printed alloys, including heterogeneous grain structures, and intragranular cellular structures composed of interior domain with limited dislocations and cell walls led by significant vanadium local segregation. Besides the outstanding mechanical properties at room temperature of 298 K, a giga-pascal yielding strength (> 1.1 GP) and over 40% uniform elongation were attained in the aged specimen deformed at a cryogenic temperature of 77 K, predominating the mechanical properties of many alloys reported in previous works. Such exceptional performance of the aged alloy can be mainly ascribed to considerable local chemical orders (LCOs), aggravated elemental fluctuation in the alloy matrix, and intensified vanadium segregation at walls of intragranular cellular structures which can strongly interact with dislocations. As a result, a planar slip array of dislocations with an extremely high density, namely large numbers of slip bands that can sustain and transfer high strains, dominates the deformation microstructures, thus efficiently strengthening and toughening the aged alloy, especially at a low temperature like 77 K. The above post-ageing strategy is readily and low-costly employed on additively manufactured MCAs with relatively high stacking fault energy (SFE) and proved as a feasible method to produce high-performance structural materials for extreme conditions.

Residual stress release and corresponding microstructural changes in high-energy impact-modified GH4169 after aging at 425 °C and 650 °C

The nickel-based superalloy is a critical material in aero-engines, where enhanced durability and resistance to stress relaxation are essential. This study evaluates the effectiveness of a high-energy composite modification technique, applied through dual surface friction methods, to induce residual stress and examines the stability of this stress under medium-temperature aging conditions. GH4169 was selected and a foundational study was conducted to quantify residual stress relaxation under medium-temperature aging treatment. The surface strengthening method used was a high-energy composite modification known for its significant post-treatment effects. The specific temperatures for medium-temperature aging treatment were 425 °C and 650 °C. The test results of the residual stress field confirmed the phenomenon of residual stress relaxation under the influence of temperature. Correspondingly, the different degrees of stress relaxation caused by varying aging treatment conditions are closely related to the microstructural changes within the material. Areas with a higher number of annealing twins exhibited a more pronounced degree of residual stress relaxation. By elucidating the link between stress relaxation and microstructural changes, this research offers a theoretical foundation for optimizing surface-strengthening processes and setting optimal operational temperatures for advanced structural materials.

Treatment of Mid-Face Aging with Calcium Hydroxylapatite: Focus on Retaining Ligament Support

Treatment of Mid-Face Aging with Calcium Hydroxylapatite: Focus on Retaining Ligament Support

Guideline recommended statin eligibility and use among U.S. adults ages 20 to 39 years

Objective: Guidelines for statin therapy emphasize treatment of adults ages 40-75 years, with less guidance for the treatment of younger adults, ages 20-39 years. Only two class 1 recommendations for statin apply to younger adults: 1) secondary prevention and 2) severe hypercholesterolemia (LDL-C ≥ 190 mg/dL). The implementation of guidelines within this age group has not been well studied. Methods & Results: Here, we use data from the National Health and Nutrition Examination Survey (2013-2020) to estimate statin eligibility and use among US younger adults. Based on this nationally representative sample, we extrapolate that approximately 923,000 younger adults had a history of atherosclerotic cardiovascular disease, but only ∼24% were on statin. Among younger adults in the primary prevention group, we extrapolate that at least 1.09 million had severe hypercholesterolemia. To expand on this analysis, we calculated untreated LDL-C values for individuals on statin using two methods, and we estimate that only ∼11-20% of younger adults with severe hypercholesterolemia were on statin. Lastly, among untreated younger adults with a class 1 indication for statin, fewer than 25% reported that a doctor or healthcare provider had recommended cholesterol medication. Conclusion: The implementation of class 1 recommendations for statin treatment in younger adults is poor. While efforts to improve risk prediction in the young have recently received significant attention, our results indicate that identifying high risk younger adults is insufficient. We must also improve guideline-recommended treatment in this age group.

Characteristics of volatile flavor development in aged longissimus lumborum post-ultrasound treatment: 4D proteomics combined with phosphoproteomics analysis

The present study aimed to evaluate the impact of ultrasonic treatment on the development of volatile flavor compounds in beef during postmortem aging and its potential mechanism. Results showed that ultrasound treatment may cause an increase in the total content of unsaturated fatty acids, which could lead to lipid oxidation and potentially result in changes in the flavor development. Additionally, it was also found that ultrasound exacerbated protein oxidation. A total of 141 volatile compounds were obtained by SPME–GC–MS analysis, and 18 differential aroma substances (P < 0.05, VIP > 1) were obtained by orthogonal partial least squares discrimination analysis (OPLS-DA). Five key volatile flavor compounds (hexanal, nonanal, octanal, pentanal, and 1-pentanol) originating from lipid oxidation were identified according to odor activity values (OAVs). The concentration of these compounds was significantly higher in the ultrasonic treatment group compared to the non-ultrasonic group that underwent a 3-day aging process. Nine common differentially expressed proteins (DEPs) were identified through the utilization of proteomics and phosphoproteomics analysis. KEGG pathways showed that selenocompound metabolism, tryptophan metabolism and cysteine and methionine metabolism led to flavor formation during wet aging of beef after ultrasound treatment. This study provided proteomic insights into the flavor of beef aged through sonication and suggested potential links between flavor development and biological processes.

Zn interlayer-induced modifications in interfacial structure and fracture behavior of Cyclic Hot-Pressed Mg/Al laminated composites

In this study, a new type of cyclic hot pressing technology was used to prepare magnesium-aluminum composites. In order to further simplify the process, the active zinc interlayer was introduced, and the interfacial bonding strength of Mg/Al LMCs was increased by 43.25%. The traditional Mg/Al LMCs interface is mainly composed of Mg-Al IMCs (β-Mg2Al3 and γ-Mg17Al12), in which the highly regular HCP-β phase leads to brittle fracture of the material. After adding zinc layer, the interface of the composites mainly presents Al-SS, η (MgZn2) and Mg-SS phases. During the preparation process, the solid solution treatment and aging treatment occurred at the composite interface, and a chain GPII zone was formed at the interface between Al-SS and η phase. This region is mainly composed of structurally unstable η′(Al-Mg-Zn), resulting in the GP II band becoming a region rich in lattice defects and a fracture source of the composite.

Synergistic regulation of nano-precipitates and reversed austenite in titanium-free maraging steel by low-temperature solution treatment and double aging treatment

To synergistically enhance the strength and toughness of titanium-free maraging steel, a multi-scale characterization method was used to illustrate the effects of low-temperature solution treatment and double aging treatment on the microstructure of titanium-free maraging steel in this paper. After the low-temperature solution treatment and the double aging treatment, the tensile strength of titanium-free maraging steel increased from 1954 MPa to 2160 MPa and the elongation increased by 8.95 %. By the low-temperature solution treatment, the original austenite grain size of the titanium-free maraging steel was refined to 0.69 μm. The double aging treatment promoted the diffusion of Mo and Ni elements, increased the volume fraction of ω phase, Ni3Mo nano-precipitation phase and reversed austenite, and refined the size of ω phase and Ni3Mo by 14.2 % and 7.9 %, respectively. The nanoparticles of titanium-free maraging steel mainly include the ω phase, Ni3Mo and Laves phase. The strengthening mechanism of nanoparticles was quantitatively evaluated from the shear mechanism and Orowan dislocation loop mechanism. The mechanism shows that the ω phase is the main contributor to the overall precipitation strengthening. Therefore, low-temperature solution treatment and double aging treatment provide a potential solution for achieving high strength and high toughness in maraging steel.

Effect of grain size on precipitation and microstrain of nanocrystalline NiTi alloys

The effect of aging treatment on the microstructure, phase transformation behavior and mechanical properties of nanocrystalline NiTi alloy was studied. The nanocrystalline NiTi alloys with different grain sizes were acquired by cold drawing followed by annealing at 350–500 °C for 10 min. The annealed samples were aged at 250–400 °C for 48 h. The Ti3Ni4 precipitates were found in aged nanocrystalline NiTi alloys. In the sample with smaller average nanograin size, the precipitates were found at the edge of grain boundaries and little lattice strain was shown in R phase matrix. In the sample with larger average grain size, the precipitates were found in the nanograins and exhibited a coherent interface with the matrix. The nanocrystalline R phase NiTi matrix exhibited a significant compressive stress at the end of the coherent precipitate. The coherent precipitates in sample aged at 250 °C after annealing at 500 °C suppress the stress-induced R → B19′ phase transformation and increased the upper plateau stress. The precipitation in sample aged at 250 °C after annealing at 350 °C unable to suppress the martensitic transformation effectively.

Microstructure, mechanical properties and deformation behavior of laser additively repaired 5083 and 6061 Al alloys utilizing AlMgScZr powders

Laser additive repair (LAR), as an efficient repair method, lacks specialized repair materials for Al alloys. In this work, the high-strength AlMgScZr powder was employed to address the scarcity of specialized materials and the issue of inadequate performance in LAR of 5083-H112/6061-T6 Al alloy. The microstructure, mechanical properties and deformation behavior of repaired specimens were studied. The repair zone (RZ) had high strength and high density, and the porosity was as low as 0.12 %. There was good compatibility between the repair material and the base metal (BM), and good metallurgical bonding was achieved at the fusion line. The microstructure and strengthening phase (T-phase) in the heat affected zone (HAZ) of the 5083 repaired parts exhibited negligible changes, there was no deterioration in mechanical properties. The yield strength was 162 MPa, tensile strength was 291 MPa, and elongation was 16.2 %, reaching 94 %, 104 %, and 70 % of the BM, respectively. The mechanical properties are superior in the current research on LAR of Al alloys. The LAR technique showcases its versatility in repairing aging non-strengthening Al alloys. The transition of β′′→β′ (or with B′/U1/U2)→β of the nano-reinforced phase resulted in deteriorative mechanical properties of HAZ in the 6061 repair part, consequently, the tensile strength of 6061 repair part was only 63.8 % of the strength of BM. After solution aging treatment, the β′′ phase in HAZ re-precipitated, effectively restoring the strength of 6061 repaired parts. The tensile strength of the repaired parts was increased to 95.2 % of the strength of BM. The present study elucidates the evolution of microstructure and mechanical properties during LAR process of Al alloys, offering valuable insights for future applications of this technology on Al alloys.

Tensile Strength Property with PdCo-Cu Multi-Layer Lamination and Heat Treatment of MEMS Probe for Probe Card

Cantilever wire probe card has limited to transport high-speed signal because of long wire but it is suitable for inspecting high-current and high voltage semiconductor such as wide band gap (WBG) power semiconductors.Superior mechanical property of a probe card wire is in demand because it is respectively used wafer inspection with in and out pad on the top surface of the power semiconductor wafer. Therefore, in this study, tensile specimens of micro electro-mechanical systems (MEMS) probe alternatively layered and electroplated with palladium (Pd)-cobalt (Co) alloy layers and copper (Cu) layers. MEMS probe was also measured tensile strength and elongation with multi-lamination and heat treatment conditions. Additionally, fractography of fracture surface after tensile test were analyzed using a scanning electron microscope (SEM). As the number of PdCo-Cu multi-layer increased, 11, 15 and 21 layered specimens showed higher tensile strength and longer elongation than 5 layered specimens because of the increase of laminated interface of PdCo and Cu. 7 layered specimen after isothermal aging had higher tensile strength and longer elongation than before isothermal aging. In 5, 11, 15 and 21 layered specimens, the fracture surfaces of tensile test specimens without aging treatment showed a ductile-brittle mixed fracture mode. Fracture surfaces of 7-layered specimen before and after isothermal aging showed a ductile-brittle mixed fracture mode.

The impact of abutment type on abutment screw removal torque value after experimental aging.

To evaluate the changes in abutment screw removal torque value (RTV) of anatomic, original hybrid, and non-original hybrid abutments after simulated clinical use. Ninety-three implant-abutment-crown specimens were divided into groups according to abutment types (n=31): anatomic (stock) (A), original hybrid (OH), and non-original hybrid (NOH). After the initial abutment screw tightening, the specimens were subjected to five screw tightening (insertion/removal) cycles, or to 5000 thermal cycles with 500,000 chewing cycles combined with one or five screw tightening cycles. RTV measurements and surface analysis using scanning electron microscope were performed before and after aging. The impact of abutment types and aging treatments on RTV was determined using two-way repeated measures ANOVA, data were described with mean±SD and range, whereas the differences were significant at p<0.05. A significant interaction was found between abutment types and screw tightening cycles only (p=0.036) or combined with thermomechanical aging (p<0.001) on RTV. RTV was lower in NOH than in A and OH groups after screw tightening and thermomechanical aging (p<0.05). Before aging, the NOH abutment screw was slightly more damaged than OH and A abutment screws. After aging, screw damage was more pronounced on the surfaces of hybrid abutments, and more evident in the NOH group. The abutment screw RTV of anatomic, original hybrid, and non-original hybrid abutments become significantly lower after abutments undergo screw tightening and/or thermomechanical aging cycles, with higher RTV loss in hybrid abutments, especially non-original ones.