The effect of TGF-beta 1 on cell proliferation and proteoglycan production in human melanoma cells depends on the degree of cell differentiation

The light-activated drugs AlPcS4 and T4MPyP were studied in a pancreatic carcinoma cell line for their effects on DNA integrity, cell division, proliferation, and survival. The micronucleus assay measured nuclear changes and also the number of actively dividing cells while, under similar conditions, the MTT assay measured cell survival. When tumour cells were exposed to light, pre-treatment with AlPcS4 induced more micronuclei than did T4MPyP at the same levels of cell division and survival. Both drugs showed a correlation between phototoxicity and changes to DNA integrity so establishing micronuclei formation as an important indicator of photodynamic drug action on tumour cells.     

Glandular odontogenic cyst: report of a case and review of the literature

The reactions of hydroxylamine 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine hydrochloride (TEMPONE-H) with peroxynitrite, superoxide and peroxyl radicals were studied. It was shown that under these reactions TEMPONE-H is oxidized into a stable nitroxide 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidi-noxyl (TEMPONE). The reactivity of TEMPONE-H towards reactive oxygen species was compared with the spin traps DMPO and TMIO as well as with DMSO and SOD. The rate constants of reactions of TEMPONE-H with peroxynitrite and superoxide radicals were 6 x 10(9) M(-1)s(-1) and 1.2x10(4) M(-1)s(-1), respectively. Using TEMPONE-H the sensitivity in the detection of peroxynitrite or superoxide radical was about 10-fold higher than using the spin traps DMPO or TMIO. Thus, TEMPONE-H may be used as a spin trap in chemical and biological systems to quantify peroxynitrite and superoxide radical formation.     

The ratio of formation of prostacyclin/thromboxane A2 in HUVEC decreased in each subsequent passage

In this study, we analyzed the antioxidative potential (SOD-, GSH-Px-activity) and the basal, H2O2- and ATP-stimulated formation of PGI2 and TXA2 in human umbilical vein endothelial cells (HUVEC) of different passages. The subcultivation of cells partly represents the process of aging. Both subcultivation of the cells and the H2O2 incubation did not significantly influence the activity of SOD and GSH-Px. H2O2 (0.1 mM and 1.0 mM) stimulated the generation of PGI2 and TXA2 in the cell passages time dependently. The formation ratio of PGI/TXA2 changed from 640:1 (0.1 mM H2O2) or 430:1 (1.0 mM H2O2, 40 min incubation) at the 1st passage, to 13:1 and 17:1, respectively, at the 4th passage. This resulted from the reduction of the PGI2 synthesis connected with more pronounced TXA2 formation. The same behavior was found in the basal and ATP-stimulated eicosanoid formation. Based on this, the age-dependent activation of the oxygen radical formation could be responsible for the modified eicosanoid metabolism resulting in vascular complications in the elderly.     

Anion dopant for oligosaccharides in matrix-assisted laser desorption/ionization mass spectrometry

Visible light (>470 nm) irradiation of an oxygen-saturated solution of C-phycocyanin (C-PC) in the presence of the spin trap 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) gave an ESR spectrum characteristic of the DMPO-hydroxyl radical spin adduct DMPO-OH. The signal intensities of DMPO-OH adduct were enhanced by superoxide dismutase (SOD) and partly inhibited by catalase. It was partly responsible for the production of DMPO-OH that superoxide anion radical (O.-2) dismutated to generate hydrogen peroxide (H2O2) which decomposed ultimately to generate the highly reactive .OH. In addition, it can be concluded that singlet oxygen (1O2) was an important intermediate according to the strong inhibitory action of 1,4-diazabicyclo[2.2.2]octane (DABCO) and histidine on DMPO-OH formation. The experimental results suggest that photodynamic action of C-PC proceed via both type I and type II mechanisms. Furthermore, the decay kinetics of DMPO-OH adduct, the effects of DMPO and C-PC concentrations as well as irradiation time on DMPO-OH adduct formation were also discussed. Concentration of C-PC should be an important factor to influence the ESR signal intensities of DMPO-OH. Therefore, it may be concluded that reasonably lower concentration of C-PC might prolong the duration of photosensitized formation of .OH and might strengthen the photodynamic action.     

The origin of the hydroxyl radical oxygen in the Fenton reaction

There is an ongoing discussion in the chemical literature regarding the nature of the highly reactive hydroxyl radical formed from the reaction between ferrous iron and hydrogen peroxide (the Fenton reaction). However, the fundamental experiment of directly determining the source of the hydroxyl radicals formed in the reaction has not yet been carried out. In this study, we have used both hydrogen peroxide and water labeled with 17O, together with ESR spin trapping, to detect the hydroxyl radicals formed in the reaction. ESR experiments were run in phosphate buffer with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap, and either H2O2 or H2O labeled with 17O. The hydroxyl radical was generated by addition of Fe2+ ion to H2O2, or as a control, by photolysis of H2O2 in the ESR cavity. Observed ESR spectra were the sum of DMPO/.16OH and DMPO/.17OH radical adduct spectra. Within experimental accuracy, the percentage of 17O-labeled hydroxyl radical trapped by the DMPO was the same as in the original hydrogen peroxide, for either method of hydroxyl radical generation, indicating that the trapped hydroxyl radical was derived exclusively from hydrogen peroxide and that there was no exchange of oxygen atoms between H2O2 and solvent water. Likewise, the complementary reaction with ordinary H2O2 and 17O-labeled water also showed that none of the hydroxyl radical was derived from water. Our results do not preclude the ferryl intermediate, [Fe = O]2+ reacting with DMPO to form DMPO/.OH if the ferryl oxygen is derived from H2O2 rather than from a water ligand.     

高性能碱土耐热镁合金的显微组织和蠕变性能

利用光学显微镜(OM),扫描电镜(SEM)及透射电镜(TEM)系统研究了碱土元素Sr和Ca加入Mg-4Al基合金后的显微组织,并测试了其抗蠕变性能.实验合金的铸态组织均由α-Mg和沿枝晶界分布的第二相组成.2%Sr加入基体合金中能观察到沿晶界的离异共晶和层片共晶Al₄Sr相及块状三元τ相.2%Ca的加入则形成了晶界层片Mg₂Ca共晶和晶内的Al₂Ca颗粒.而在Mg-4Al-2Sr-1Ca中,晶界相为块状τ相和层片状Mg₂Ca共晶,晶内也析出Al₂Ca颗粒.在Mg-4Al-2Sr-1Ca基础上提高Al含量,粗大不规则共晶(Mg,Al)₂Ca相在晶界处形成并不断增多,Mg₂Ca及τ相逐渐减少,当Al含量到7%时,出现了新的细小层片状Al₄Sr相.Sr、Ca元素加入Mg-Al合金,改善了合金的抗蠕变性能,其中Mg-5Al-2Sr-1Ca和Mg-6Al-2Sr-1Ca合金显示所有实验合金中最好的蠕变抗力.根据Power-law公式,在175℃/50~80MPa和70MPa/150~200℃蠕变下,Mg-4Al-2Sr合金在较低应力(<60MPa)下蠕变表现为扩散控制的位错攀移机制,而在高应力下出现Power-law公式的失效;Mg-4Al-2Sr-1Ca合金蠕变则受到了扩散控制的位错机制和晶界滑移机制的共同作用.     

Efficacy of systemic administration of irinotecan against neuroblastoma xenografts

4-Hydroxytamoxifen is a major metabolite of the antiestrogenic drug tamoxifen used in the treatment of women with breast cancer. 4-Hydroxytamoxifen is broken down by a horseradish peroxidase/H2O2 system very much more rapidly than tamoxifen and causes much greater DNA damage determined by 32P-postlabelling. EPR spin trapping of 4-hydroxytamoxifen reaction products in the presence of the free radical trap 5,5-dimethyl-1-pyrroline N-oxide, together with glutathione as a hydrogen donor, resulted in the generation of a species with the characteristics of the glutathione thiyl radical (aN approximately 15.3 G, aH approximately 16.2 G). Support for the creation of thiyl radicals comes from the close to stoichiometric time dependent formation of glutathione disulfide concomitant with the loss of glutathione. Similar results were obtained using 4-hydroxytoremifene but no radical formation or glutathione loss could be detected using 3-hydroxytamoxifen (droloxifene). On-line LC-ESI MS analysis of the incubation products from 4-hydroxytamoxifen has identified three products with a protonated molecular mass of 773, consistent with the formation of dimers of 4-hydroxytamoxifen. The role that radical mechanisms have in the carcinogenic effects of tamoxifen in the endometrium or other target organs of women taking this drug remains to be established.     

超音速等离子喷涂Al-35Si-4Fe涂层制备工艺优化及摩擦学性能

为改善铝硅合金的摩擦学性能,以YL113铝硅合金为基体,喷涂功率、总气流量和喷涂距离为试验因素,显微硬度和孔隙率为考核指标,采用三因素三水平的正交试验法得到了超音速等离子喷涂Al-35Si-4Fe涂层的最佳制备工艺;研究了此工艺下涂层的摩擦学性能。结果表明：喷涂功率为65 kW,总气流量为110 L/min,喷涂距离为95 mm时,涂层质量为最佳。此时,Al-35Si-4Fe涂层的显微硬度达到465±24.4 HV0.2,涂层孔隙率为1.3%。实验条件下,Al-35Si-4Fe涂层的磨损机制以疲劳磨损为主,磨粒磨损为辅。Al-35Si-4Fe涂层的磨损率为1.88 ×10-4 ^mm3^/Nm,摩擦因数为0.37。优化后的Al-35Si-4Fe涂层能有效保护内部YL113铝硅合金,延长其使用寿命,并应对更加复杂的工况。     

Fructose metabolism and cell survival in freshly isolated rat hepatocytes incubated under hypoxic conditions: proposals for potential clinical use

The protective effect of fructose with regard to hypoxia-induced cell injury was investigated. The addition of fructose (2 to 20 mmol/L) protected hepatocytes against hypoxia-mediated cell lysis in a concentration-dependent way. The intracellular ATP content was initially decreased as a result of fructose-1-phosphate formation, but it remained constant during the hypoxic incubation. Conversely, high initial ATP values observed at low fructose concentrations progressively declined. Cellular protection was observed only when fructose was added before (and not after) the start of hypoxia. In addition, a sufficient amount of fructose-1-phosphate rapidly accumulated before the induction of hypoxia, and the linear production of lactate, during hypoxic incubation, indicated that cells synthesized ATP continuously. The lack of cell protection by fructose added after the onset of the hypoxia may be explained by a lesser fructose-1-phosphate formation and a subsequently low accumulation leading to insufficient glycolytic ATP production. Under aerobic conditions, both glycolysis (lactate formation) and gluconeogenesis (glucose formation) were carried out in fructose-1-phosphate-loaded cells with the same initial rates, whereas under hypoxic conditions glycolysis was the main metabolic event. The fact that protein synthesis activity recovered faster during reoxygenation of previously hypoxic fructose-treated cells than in glucose-treated cells led us to hypothesize that in situ perfusion of liver with fructose, before its removal, would improve its metabolic capacity during the hypoxic cold preservation and subsequent transplantation.     

Distribution and photodynamic effect of zinc phthalocyanine disulfonate in nude mice bearing mammary carcinoma

The distribution study of zinc phthalocyanine disulfonate (ZnPcS2) in nude mice bearing mammary carcinoma (T50/80) revealed a rapid uptake of the dye by tumor. In experimental photodynamic therapy (PDT), the tumors were exposed to laser radiation (670 nm, 100 mW/cm2, 150 J/ /cm2) after intravenous administration of ZnPcS2 in saline. The results showed the maximum tumor destruction to be achieved for the time interval between injection of the drug (2 mg/kg) and exposure to laser light of 5 min, while a significantly less damage was observed when the time interval was 24 h (p < 0.0001). The degree of damage produced by the treatment was monitored in vivo by means of noninvasive NMR-imaging and subsequently confirmed histologically.     

Spin trapping of azidyl and hydroxyl radicals in azide-inhibited rat brain submitochondrial particles

Succinate-driven respiration in azide-inhibited rat brain submitochondrial particles (smps) produces azidyl and hydroxyl radicals that were detected by spin trapping with 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Production of radicals required succinate and oxygen and was eliminated by heat denaturation, which indicates that radical production is a result of respiration. The concentrations of both DMPO/.OH and DMPO/.N3 were decreased by addition of catalase to the smps, which indicates that H2O2 is involved in radical production. In the absence of azide anion, DMPO/.OH was not detected in the same system, even after five additions of succinate over a period of 24 h. It is proposed that azide inhibition of cytochrome c oxidase results in increased production of superoxide, which is efficiently converted to hydrogen peroxide by membrane-bound superoxide dismutase. Hydrogen peroxide activates endogenous peroxidase to react with azide anion forming azidyl radical, which damages the peroxidase, resulting in decreased production of azidyl radical with successive additions of succinate. Hydroxyl radical is produced from the hydrogen peroxide that is not removed by peroxidase. The increased production of superoxide in the azide-inhibited system suggests that loss of cytochrome c oxidase activity can lead to increased radical production if other proteins in the respiratory chain remain active. In the azide-inhibited system, reaction of azide anion with H2O2-activated endogenous peroxidase and spin-trapping of the resulting azidyl radical is a convenient monitor of H2O2 production.     

Lethal photosensitisation of Staphylococcus aureus in vitro: effect of growth phase, serum, and pre-irradiation time

BACKGROUND AND OBJECTIVES: Staphylococcus aureus can be killed by low-power laser light in the presence of aluminium disulphonated phthalocyanine (AlPcS2). The purpose of this study was to determine the effect of pre-irradiation time (PIT), the presence of serum, and the physiological state of the organism on the kills achieved. STUDY DESIGN/MATERIALS AND METHODS: To determine the effect of PIT on killing, suspension of methicillin-resistant S. aureus (MRSA) were incubated in the dark with 12.5 micrograms/ml of AlPcS2 for 60 s or 300 s, and survivors were enumerated after exposure to 1.2 J of light from an 11-mW gallium aluminium arsenide laser. The susceptibility of MRSA in its various growth phases was determined in a similar manner using a PIT of 300 s. The effect of serum on killing was determined using stationary phase cells resuspended in horse serum. RESULTS: Using a PIT of either 60 s or 300 s, 10(6) cfu (99.9%) of MRSA were killed. There was little difference in the susceptibility of lag-, logarithmic-, or stationary-phase cells, the kills being 99.9%, 99.8%, and 99.9%, respectively. Although kills were reduced in the presence of serum, 99.6% of MRSA were killed using a light dose of 1.2 J. CONCLUSION: These results demonstrate that MRSA can be rapidly sensitised by AlPcS2 to killing by low-power laser light, that killing is not dependent on the organism's growth phase, and that substantial kills can be achieved in the presence of serum.     

Management of combined penetrating cardiac and abdominal trauma

Detection of hydroxyl free radicals is frequently performed by electron spin resonance (ESR) following spin trapping of the radical using 5,5-dimethylpyrroline N-oxide (DMPO) to generate a stable free radical having a characteristic ESR spectrum. The necessary ESR equipment is expensive and not readily available to many laboratories. In the present study, a specific and sensitive gas chromatography-mass spectrometry (GC/MS) method for detection of hydroxyl and hydroxyethyl free radicals is described. The DMPO or N-t-butyl-alpha-phenylnitrone (PBN) radical adducts are extracted and derivatized by trimethylsylilation and analyzed by GC/MS. To standardize the method, .OH and 1-hydroxyethyl radicals were generated in two different systems: 1) a Fenton reaction in a pure chemical system in the absence or presence of ethanol and 2) in liver microsomal suspensions where ethanol is metabolized in the presence of NADPH. In the Fenton system both radicals were easily detected and specifically identified using DMPO or PBN. In microsomal suspensions DMPO proved better for detection of .OH radicals and PBN more suitable for detection of 1-hydroxyethyl radicals. The procedure is specific, sensitive and potentially as useful as ESR.     

Calcium vs. iron-mediated processes in hydrogen peroxide toxicity to L929 cells: effects of glucose

H2O2 toxicity was studied in L929 cells in the presence and absence of glucose. The data obtained in the absence of glucose suggest a Ca2+-dependent mechanism of cell injury. No evidence was found for any involvement of iron in the process. In particular, cell injury was unaffected by the intracellular iron chelators 2,2'-dipyridyl and deferoxamine or by the hydroxyl radical scavengers DMSO and DMPO. On the other hand, the intracellular Ca2+ chelator BAPTA/AM provided significant protection. The cytosolic Ca2+ level rapidly and consistently increased after H2O2 addition, prior to visible bleb formation and loss of cell viability. Additionally, GSH not only prevented cell death but also significantly decreased cytosolic calcium accumulation. In the presence of glucose, however, Ca2+ does not seem to play any role in H2O2 toxicity. Cell death is now mainly mediated by iron: the iron chelators and hydroxyl radical scavengers prevented cell injury, the increase in cytosolic Ca2+ was significantly less pronounced, and BAPTA/AM did not exert any protection under these conditions. Hence, the metabolic state of the L929 cells, as given by the availability of glucose, decisively determines the biochemical mechanism of H2O2 cell injury.     

Activity wheel running blunts increased plasma adrenocorticotrophin (ACTH) after footshock and cage-switch stress

N'-(3'-Monophospho-deoxyguanosin-8-yl)-N-acetylbenzidine (dGp-ABZ) is thought to play an important role in initiation of benzidine-induced bladder cancer in humans. This report assesses the possible formation of this adduct by peroxidatic activation of N-acetylbenzidine (ABZ). Adduct formation was measured by 32P-post-labeling. Ram seminal vesicle microsomes were used as a source of prostaglandin H synthase (PHS). The peroxidatic activity of PHS was compared with that for horseradish peroxidase. Both peroxidases converted ABZ to dGp-ABZ whether DNA or 2'-deoxyguanosine 3'-monophosphate (dGp) was present. Following 32P-post-labeling, the enzymatic and synthetic adduct were extracted from PEI-cellulose plates and were shown to have the same HPLC elution profiles for the bisphosphate adduct (32P-dpGp-ABZ). Treatment of the enzymatic and synthetic bisphosphate adduct with nuclease P1 yielded a product that eluted at the same time from the HPLC (32P-dpG-ABZ). Additional experiments demonstrated that the PHS-derived 5'-monophosphate (dpG-ABZ) and 3'-monophosphate (dGp-ABZ) adducts were also identical to their corresponding synthetic standard. With comparable amounts of total ABZ metabolism, PHS produced approximately 40-fold more dGp-ABZ than horseradish peroxidase (1943 +/- 339 versus 49 +/- 7.8 fmol/mg dGp). Adduct formation was dependent upon the presence of peroxidase and the specific substrate, i.e. arachidonic acid or H2O2. Adduct formation by PHS was inhibited by indomethacin (0.1 mM), ascorbic acid (1 mM) and glutathione (10 mM), but not by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) (100 mM), a radical scavenger. Horseradish peroxidase adduct formation was also inhibited by ascorbic acid and glutathione. In addition, DMPO elicited greater than a 96% inhibition. Results demonstrate peroxidatic metabolism of ABZ to form dGp-ABZ. The mechanism of dGp-ABZ formation by PHS and horseradish peroxidase may be different.     

A role for oxygen radicals in rat monocytic leukemia cell differentiation under stimulation with platelet-activating factor

Combined stimulation, by superoxide ions generated by the xanthine-xanthine oxidase reaction, and platelet-activating factor (PAF), induced cell differentiation of rat monocytic leukemia cells (c-WRT-LR) to macrophage-like mature cells. Monitoring of cytochrome c reduction revealed that PAF stimulation induced the release of superoxide ions from c-WRT-LR. To further investigate the effect of superoxide ions in the autocrine or paracrine mechanism in cell differentiation, molecular species of the oxygen radicals under PAF stimulation were examined using the EPR spin trap, 5,5'-dimethyl-1-pyrroline N-oxide (DMPO). PAF and/or phorbol myristate acetate caused the formation of EPR spectra, a combination of DMPO/.OOH and DMPO/.OH. Since both spectra were diminished in the presence of superoxide dismutase, it was concluded that DMPO/.OH was derived from superoxide ions. Mannitol and catalase suppressed cell differentiation induced by combined stimulation with PAF and oxygen radicals generated by the xanthine-xanthine oxidase reaction. Taken together, these results suggest that hydroxyl radicals generated by Fenton reaction from H2O2 may be involved in the mechanism of cell differentiation in rat monocytic leukemia cells.     

Early endothelial alterations in non-insulin-dependent diabetes mellitus

Nude mice were given AlPcS2a (aluminum phthalocyanine disulfonate) and AlPcS4 (aluminum phthalocyanine tetrasulfonate) by intraperitoneal injections. After time intervals of 1-48 hours the mice were exposed to 150 mW cm-2 light at 670 nm and the phthalocyanine fluorescence was measured during light exposure. During the first few minutes of light exposure the phthalocyanine fluorescence of the skin of the mice increased by up to a factor of two, indicating lysosomal localization of the dye and permeabilization of the lysosomes. The process did not occur in the skin of dead mice, indicating that the process was dependent on oxygen.     

Overexpression of human superoxide dismutase inhibits oxidation of low-density lipoprotein by endothelial cells

Oxidation of LDL in the subendothelial space has been proposed to play a key role in atherosclerosis. Endothelial cells produce superoxide anions (O2.-) and oxidize LDL in vitro; however, the role of O2.- in endothelial cell-induced LDL oxidation is unclear. Incubation of human LDL (200 microg/mL) with bovine aortic endothelial cells (BAECs) for 18 hours resulted in a 4-fold increase in LDL oxidation compared with cell-free incubation (22.5+/-1.1 versus 6.3+/-0.2 [mean+/-SEM] nmol malondialdehyde/mg LDL protein, respectively; P<0.05). Under similar conditions, incubation of LDL with porcine aortic endothelial cells resulted in a 5-fold increase in LDL oxidation. Inclusion of exogenous copper/zinc superoxide dismutase (Cu/ZnSOD, 100 microg/mL) in the medium reduced BAEC-induced LDL oxidation by 79%. To determine whether the intracellular SOD content can have a similar protective effect, BAECs were infected with adenoviral vectors containing cDNA for human Cu/ZnSOD (AdCu/ZnSOD) or manganese SOD (AdMnSOD). Adenoviral infection increased the content and activity of either Cu/ZnSOD or MnSOD in the cells and reduced cellular O2.- release by two thirds. When cells infected with AdCu/ZnSOD or AdMnSOD were incubated with LDL, formation of malondialdehyde was decreased by 77% and 32%, respectively. Two other indices of LDL oxidation, formation of conjugated dienes and increased LDL electrophoretic mobility, were similarly reduced by SOD transduction. These data suggest that production of O2.- contributes to endothelial cell-induced oxidation of LDL in vitro. Furthermore, adenovirus-mediated transfer of cDNA for human SOD, particularly Cu/ZnSOD, effectively reduces oxidation of LDL by endothelial cells.     

Brazing of Ti-6Al-4V and niobium using three silver-base braze alloys

Evaluations of the (infrared)-brazed Ti-6Al-4V and niobium joints using three silver-base braze alloys have been extensively studied. According to the dynamic wetting angle measurement results, the niobium substrate cannot be effectively wetted by all three braze alloys. Because the dissolution of Ti-6Al-4V substrate causes transport of Ti into the molten braze, the molten braze dissolved with Ti can effectively wet the niobium substrate during brazing. For infrared-brazed Ti-6Al-4V/Ag/Nb joint, it is mainly comprised of the Ag-rich matrix. The TiAg reaction layer is observed at the interface between the braze and Ti-6Al-4V substrate. In contrast, Ti-rich, Ag-rich, and interfacial TiAg phases are found in the furnace-brazed specimen. The dominated Ti-rich phase in the joint is caused by enhanced dissolution between the molten braze and Ti-6Al-4V substrate. The infrared-brazed Ti-6Al-4V/72Ag-28Cu/Nb joint is mainly comprised of the Ag-rich matrix and Ag-Cu eutectic. With increasing the brazing temperature or time, the amount of Ag-Cu eutectic is decreased, and the interfacial Cu-Ti reaction layer(s) is increased. The infrared brazed joint has the highest average shear strength of 224.1 MPa. The averaged shear strength of the brazed joint is decreased with increasing brazing temperature or time, and its fracture location changes from the braze alloy into the interfacial reaction layer(s) due to excessive growth of the Cu-Ti intermetallics. The infrared-brazed Ti-6Al-4V/95Ag-5Al/Nb joint is composed of Ag-rich matrix and TiAl interfacial reaction layer. With increasing the brazing time, the amount of Ag-rich phase is greatly decreased, and the interfacial reaction layer becomes Ti₃Al due to enhanced dissolution of Ti-6Al-4V substrate into the molten braze. The average shear strength of the infrared-brazed joint is 172.8 MPa. Additionally, the existence of an interfacial Ti₃Al reaction layer significantly deteriorates the shear strength of the furnace-brazed specimen.     

Ti-Al-Nb-W基合金高温变形过程中的组织演化

在Thermecmastor-Z动态热模拟试验机上对Ti-43Al-4Nb-1.4W和Ti-43Al-4Nb-1.4W-0.6B-0.2Y合金进行高温压缩变形实验(实验温度范围为1 050~1 150℃,应变速率范围为0.001~1 s 1),对其热变形组织进行显微分析,并利用热加工Z参数(Zener-Hollomon参数)综合描述变形温度及应变速率对材料热变形行为的影响。结果表明:2种合金在不同高温压缩变形条件下均发生不同程度的动态再结晶;随Z参数值的降低,β相逐渐由不规则形状转变为球形,且长大明显,同时,动态再结晶晶粒的体积含量也随之增加;Ti-43Al-4Nb-1.4W基合金的高温变形机制与Z参数值密切相关;在低Z值条件下,其主要变形机制为动态再结晶和β相的球化、长大;在高Z值条件下,其主要变形机制为片层的扭折、重新取向和局部动态再结晶;加入微量B和Y后,动态再结晶程度增大,这主要与颗粒诱发动态再结晶形核有关。