Misfit as a characteristic of the level of interfacial stresses in single-crystal nickel superalloys

A method for determining the level of interfacial stresses in single-crystal nickel superalloys and the results of its determination are presented. The splitting of the (h00) X-ray diffraction peaks in the X-ray diffraction patterns of the γ and γ′ phases that is caused by interfacial thermal stresses is studied.     

Wettability and interfacial behaviour of NdF3-LiF-Nd2O3 on TiB2-based ceramics

Wettability of TiB2-based ceramics by NdF3-LiF-Nd2O3 melt was studied using sessile drop technique in this paper. Wetting ex-periment was carried out under inert atmosphere at 1050 ℃. Chemical reactions which occurred on the solid-liquid interface and solid-gas interface during wetting process were discussed by thermodynamic calculations combined with X-ray diffraction (XRD) patterns. Micromorphoiogy and element distribution of fracture surface at the interfacial region of solid/liquid system were analyzed by scanning elec-tron microscope (SEM) equipped with energy dispersive spectrometry (EDS). Contact angles of the drop were determined as a function of time in order to describe the wetting process, and wetting phenomenon was interpreted fi'om a viewpoint of interface structure. The results showed that wetting was a dynamic wetting process with characteristics of reactive wetting. Penetration and oxidization phenomena during the experiment had great effect on wetting process.     

Ceramic cups for hip endoprostheses. 3: On the problem of osseointegration of monolithic cups

The combination of ceramic with ceramic offers the option of minimising wear and the need for revision in total hip replacement. At first, uncemented monolithic ceramic sockets were implanted. Some of these did not prove successful. The prerequisites for fixation of an implant by bony integration are discussed i.e. the structural and surface compatibility of an implant. The reasons for the high revision rate associated with monolithic ceramic sockets are discussed. Using monolithic ceramic sockets only contact osteogenesis can in principle be achieved, which does not suffice for good long-term fixation. In many cases, soft tissue can be found at the ceramic socket/bone interface, and the ceramic sockets may as a result migrate and penetrate, creating conditions that elevate the rate of wear to unacceptable levels.     

Estimated content percentages of volatile liquids and fat extractables in ready-to-eat foods

Content percentages of volatile liquids and fat extractables in 340 samples of ready-to-eat foods were determined gravimetrically. Volatile liquids were determined by drying samples in a microwave oven with a self-contained balance; results were printed out automatically. Fat extractables were extracted from the samples with mixed ethers; extracts were dried and weighed manually. The samples, 191 nonfat and 149 fatty (containing ca 2% or more fat) foods, represent about 5000 different food items and include infant and toddler, ethnic, fast, and imported items. Samples were initially prepared for screening of essential and toxic elements and chemical contamination by chopping and mixing into homogenous composites. Content determinations were then made on separate portions from each composite. Content results were put into a database for evaluation. Overall, mean results from both determinations agree with published data for moisture and fat contents of similar food items. Coefficients of variation, however, were lower for determination of volatile liquids than for that of fat extractables.     

Residual stresses and their effects on deformation

Residual stresses induced by thermal expansion mismatch in metal-matrix composites are studied by three-dimensional (3-D) elastic-plastic finite element analyses. Typically, the stress-free state is 150 to 300 K above room temperature. The coefficient of thermal expansion of the matrix is 3 to 5 times larger than that of the ceramic inclusion, resulting in compressive stresses of order 200 MPa in the inclusions. Both compressive and tensile stresses can be found in the matrix. Since the stress may exceed the matrix yield strength near the particles, plastic flow occurs. The authors find a significant influence of this flow on the elastic and plastic properties of the composite. The calculated residual strains in TiC particles due to thermal expansion mismatch and external loads compare well with recent neutron diffraction experiments (Bourkeet al.) The present work is the first reported three-dimensional analysis of spherical inclusions in different arrays (simple cubic (sc) and face-centered cubic (fcc)) that permit a study of particle interactions.     

Effects of irradiation on osseointegration before and after implant placement: a report of three cases

Three patients irradiated as a part of cancer treatment, both before and after placement of endosseous implants, were studied. Total irradiation doses varied from 80 to 195 Gy in the tumor/implant area. Implants failed at a rate of 64.2% during a 3-year follow-up period. All patients developed osteoradionecrosis in the tumor cavities adjacent to the implants. The combined effects of the pre- and postoperative irradiation, in conjunction with the placement of implants, appear to challenge the limits of osseointegration. Until further knowledge is obtained regarding how such highly radiated tissue should be handled, it is recommended that if anchorage of craniofacial prostheses is attempted according to osseointegration principles, it should be performed with the utmost care.     

Effect of uniaxial stresses on sintering shrinkage

Translated from Poroshkovaya Metallurgiya, No. 11(311), pp. 11–13, November, 1988.     

Influence of ash on interfacial reactions between coke and liquid iron

Interfacial reactions occurring between molten iron and carbonaceous materials are of great significance in the steel industry, and specifically, the reaction of iron with metallurgical coke is one of the key phenomena occurring during blast furnace ironmaking. Major operating parameters such as hot metal composition will be directly influenced by the reactions occurring between liquid iron and coke. In the current investigation, the interfacial reactions occurring between coke and liquid iron were studied at a temperature of 1550 °C using the sessile drop method to further the understanding of the fundamental reactions occurring at the interface between coke and iron. The formation of interfacial reaction products was observed, and time-dependent reactions were identified. The transfer of elements such as carbon, sulfur, and silicon was determined. The reduction of silica was determined as having a major influence on the transfer of both silicon and carbon into liquid iron. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Influence of interfacial reactions on the fiber-matrix interfacial shear strength in sapphire fiber-reinforced Nial(Yb) composites

The influence of microstructure of the fiber-matrix interface on the interfacial shear strength, measured using a fiber-pushout technique, has been examined in a sapphire-fiber-reinforced NiAl(Yb) matrix composite under the following conditions: (1) as-fabricated powder metallurgy (PM) composites, (2) PM composites after solid-state heat treatment (HT), and (3) PM com-posites after directional solidification (DS). The fiber-pushout stress-displacement behavior con-sisted of an initial “pseudoelastic” region, wherein the stress increased linearly with displacement, followed by an “inelastic” region, where the slope of the stress-displacement plot decreased until a maximum stress was reached, and the subsequent gradual stress decreased to a “fric-tional” stress. Energy-dispersive spectroscopy (EDS) and X-ray analyses showed that the inter-facial region in the PM NiAl(Yb) composites was comprised of Yb₂O₃,O-rich NiAl and some spinel oxide (Yb₃Al₅O₁₂), whereas the interfacial region in the HT and DS composites was comprised mainly of Yb₃Al₅O₁₂. A reaction mechanism has been proposed to explain the pres-ence of interfacial species observed in the sapphire-NiAl(Yb) composite. The extent of inter-facial chemical reactions and severity of fiber surface degradation increased progressively in this order: PM < HT < DS. Chemical interactions between the fiber and the NiAl(Yb) matrix resulted in chemical bonding and higher interfacial shear strength compared to sapphire-NiAl composites without Yb. Unlike the sapphire-NiAl system, the frictional shear stress in the sap-phire-NiAl(Yb) composites was strongly dependent on the processing conditions. Formerly Research Associate, Department of Chemical Engineering, Cleveland State University     

Elastic interaction stresses: Part II. The influence of orientation on stresses generated in iso-axial bicrystals

The effects of four types of incompability on stresses generated in seven iso-axial bicrystals of 70-30 alpha brass subjected to tension were examined by finite element methods. The distribution of applied stress and resolved shear stresses was determined. The applied stress, { }, was higher at the interior than at the surface, while the resolved shear stresses were generally higher at the surface. For both applied { } and resolved shear stresses, the largest stresses occurred at the bicrystal boundaries. The effect of end constraints on a [213] oriented single crystal was found to create nonuniform stresses and strains, and an explanation for this behavior was proposed. The effect of orientation on the magnitude of grain boundary resolved shear stress, { }, and the relative extent (volume fraction) of enhanced grain boundary resolved shear stress,V _gb, were determined. The highest values of { } andV _gb were reached in different portions of the stereographic triangle. The elastic interactions producing this behavior were too complex to permit a simple interpretation. TZI-KANG CHEN formerly Graduate Student at Polytechnic University     

Cu-Sn-Ti体系边际二元系界面反应的研究

Cu-Sn-Ti三元系及其相关的3个二元系均具有重要的实用价值.实验制备了Ti/Sn和Cu/Sn固-液扩散偶及Cu/Ti二元固相扩散偶,经电子显微和探针观测发现: Ti/Sn固-液扩散偶在873K下退火30～160min,只生成1个Sn3Ti2中间相; Cu/Sn固-液扩散偶在808K下退火10min时也只生成1个Cu3Sn中间相,但退火时间延长至30min时在Cu与Cu3Sn界面上生成Cu41Sn11,退火60min后在Cu与Cu41Sn11之间又生成了bcc-a2; Cu/Ti二元固相扩散偶在1023K下退火1000h后,在其界面处生成了CuTi2、CuTi、Cu4Ti3、Cu4Ti 4个化合物,而Cu3Ti2相并未在扩散偶中出现.还采用最大驱动力模型对上述3个二元系的界面反应过程进行了计算并成功解释了相应的实验现象.     

Effect of interfacial debonding and sliding on matrix crack initiation during isothermal fatigue of SCS-6/Ti-15-3 composites

Direct observation of initial damage-evolution processes occurring during cyclic testing of an unnotched SCS-6 fiber-reinforced Ti-15-3 composite has been carried out. The aligned fibers break at an early stage, followed by debonding and subsequent sliding along the interface between the reaction layer (RL) and Ti-15-3 alloy matrix. Matrix cracking initiation from the initial broken fiber and RL was avoided. This fracture behavior during cyclic loading is modeled and analyzed by the finite-element method, with plastic deformation of the matrix being considered. The plastic strain in the matrix at the initial crack and at the deflected crack tips, when the interface crack is deflected into the RL after extensive interface debonding propagation, is characterized. The effects of interfacial debond lengths and test temperatures on the matrix cracking mechanism are discussed, based on a fatigue-damage summation rule under low-cycle fatigue conditions. The numerical results provide a rationale for experimental observations regarding the avoidance and occurrence of the matrix cracking found in fiber-reinforced titanium composites.     

A comparative study of osseointegration of titanium implants in autogenous and freeze-dried bone grafts

PURPOSE: This study was undertaken to compare the rate and degree of osseointegration of dental implants when placed into either autogenous corticocancellous chip or freeze-dried corticocancellous chip bone grafts. MATERIALS AND METHODS: The canine ilium was used as the model site. Thirty experimental and 15 control implants were placed in 15 dogs: autogenous versus freeze-dried corticocancellous chip bone grafts around the exposed implant surfaces. In addition to the placement of control implants, the apical portion of the grafted implants acted as their own control. The implants were harvested at 1, 2, and 3 months. The evaluation of the integration process was performed by means of light microscopy, microradiography, and histomorphometry. RESULTS: Using this model, the results indicate that at 1 month there was no statistical difference in the degree of osseointegration in the two bone grafts. At 2 months, there was a statistically greater degree of osseointegration noted in the autogenous corticocancellous chip sites than in the freeze-dried bone grafts. At 3 months, the degree of osseointegration in the two groups was 70% and 33%, respectively. At 3 months, there was virtually 100% integration with trabecular bone at the control implant sites. CONCLUSION: The results indicate that at 2 months postoperatively implants placed in an autogenous bone chip graft osseointegrate to a significantly greater degree than implants placed in a freeze-dried bone chip graft, and this difference remains at 3 months.     

Effects of irradiation on the biomechanics of osseointegration. An experimental in vivo study in rats

The present study reports on the late effects of increasing doses of radiation on the biomechanics of commercially pure titanium implants (fixtures) installed in the proximal tibia in 26 rats. Twelve weeks after various doses (10, 20, 30, and 35 Gy) of irradiation, the fixtures were inserted into rat tibiae, and after another eight weeks these were tested mechanically in vivo. Acute dose dependent skin reactions developed after all doses except 10 Gy, but most subsided within two to three weeks. There was a statistically significant reduction in torsion but the pull-out load was not significantly reduced for single doses up to 30 Gy. Histological analysis showed that bone remodelling was impaired. Shear stresses and shear moduli were estimated for the bone-implant interface and in the surrounding bone tissue. These estimated stresses and moduli were not found to be correlated to the dose of radiation.     

Rate of interfacial reaction between molten CaO-SiO2-Al2O3-Fe x O and CO-CO2

Measurements of the rates of reduction of iron oxide from molten CaO-SiO₂-Al₂O₃-Fe _x O slags by Ar-CO mixtures have been made using a thermogravimetric method. The apparent first-order rate constant, with respect to the partial pressure of CO, of the gas/slag interfacial reaction was deduced from the measured rates, where the effects of the mass transfer in the gas and slag phases were minimized. It was found that the apparent first-order rate constant decreased with the concentration of ‘FeO’ from 100 to 20 wt pct, whereas it remained essentially constant in the range from 5 to 20 wt pct ‘FeO’. At a given iron oxide concentration, the reduction-rate constant increased significantly with an increase in the CaO/SiO₂ ratio. For fixed slag compositions, the reduction rate increased slightly with the oxidation state of the slags. When the rate constant is expressed in the form of k=k′(Fe³⁺/²⁺)^α, the values of α range from 0.15 to 0.25. The effect of temperature in the range from 1673 to 1873 K on the reduction rate of iron oxide in a 40.4CaO-40.4SiO₂-14.2Al₂O₃-5‘FeO’ (wt pct) slag was studied. The calculated activation energy, based on these results, is 165 kJ/mol.