Effect of nano-sized TiO<Subscript>2</Subscript> powder addition on characteristics of silver–palladium electrodes

This study presents the sintering behavior of silver/palladium electrode powders to which have been added TiO₂ nanoparticles, and the effect this additive has on the ability of the electrode to match the characteristics of piezoelectric ceramics, Pb(Zr, Ti)O₃. The densification (shrinkage) of the electrodes was investigated as a function of sintering temperature, and the reaction between the ceramic matrix and the electrodes was studied. The densification of the TiO₂-enhanced electrode paste during the sintering process was explained with reference to a solid-state diffusion mechanism which integrated the TiO₂ into the ceramic. Reactions occurred between the ceramic and electrode layers, resulting in reduced internal stress and enhanced mechanical adhesion. Based on these results, it is clear that high adhesive strength and good electrical conductivity of more than 10⁴/Ω cm can be obtained in multilayer ferroelectric devices composed of stacks of ceramic and electrode layers provided the contain these nanoparticles. In the sintering process, interfacial diffusion of TiO₂ occurred and, as a consequence, coarse grains of PZT were formed at the interface.     

The solid state bonding of nickel to alumina

The paper describes the effect of sintering atmosphere (argon, hydrogen and vacuum), sintering temperatures (700 to 1300° C), sintering pressure (1/2 to 6 tsi [7.7 to 92.4 MN. m^–2]) and sintering time (1/2 to 24 h) on the room temperature shear bond strength developed between nickel powder compacts and alumina single crystals: bond strengths of 3 to 11×10³ psi (20.7 to 75.9 MN. m^–2) were developed and are satisfactory for composite strengthening. The spinel, NiAl₂O₄ was detected at the nickel/alumina interface. Heat treatment at 1100° C for 300 h resulted in gross chemical attack, but without degeneration of the bond strength. The variations in shear strength observed are discussed in terms of the nickel grain size and porosity and the differential thermal expansion of the two components.     

Mechanical properties of single crystals of transition metals diborides TMB<Subscript>2</Subscript> (TM = Sc,Hf, Zr,Ti). Experiment and theory

The mechanical behaviour of TMB₂ whiskers (TMB₂ = Sc, Hf, Zr, Ti) of 10–20 μm in diameter of the directionally reinforced ceramics LaB₆–TMB₂ was experimentally studied by the nanoindentation. The pop-in (the abrupt elastic–plastic transition in the indenter penetration) caused by the nucleation of dislocations in the previously dislocations-free region under the imprint was observed in all samples under study. For the first time the experimental estimations of the theoretical shear strength of these materials are obtained. Zone structures and types of interatomic bonds for TMB₂ (TM= Sc, Zr, Hf, Ti) are theoretically calculated. The effects of the electronic structures on mechanical properties of diborides of transition metals were analyzed.     

Hydrothermal preparation of Ba(Ti,Zr)O3 fine powders

Fine powders consisting of aggregated submicron crystallites of Ba(Ti,Zr)O₃ in the complete range of Ti/Zr ratios are prepared at 85–130°C by hydrothermal method, starting from TiO₂ + ZrO₂ · xH₂O mixed gel and Ba(OH)₂ solution. The products obtained below 110°C incorporate considerable amounts of H₂O and OH⁻ within the lattice. As-prepared BaTiO₃ is cubic and converts to tetragonal phase after the heat treatment at 1200°C, accompanied by the loss of residual hydroxyl ions. TEM investgations of the growth features show a transformation of the gel to the crystallite. Ba²⁺ ions entering the gel produce chemical changes within the gel, followed by dehydration, resulting in a cubic perovskite phase irrespective of Ti/Zr. The sintering properties of these powders to fine-grained, high density ceramics and their dielectric properties are presented.     

Transient liquid phase diffusion bonding of continuous SiC fibre reinforced Ti–6AI–4V composite to Ti–6AI–4V alloy

Abstract

A continuous SiC fibre reinforced Ti–6Al–4V composite was diffusion bonded in transient liquid phase to Ti–6Al–4V alloy plate using Ti–Cu–Zr amorphous filler metal. Joint strength increased with bonding time up to 1·8 ks and reached the maximum value of 850 MN m^?2 which corresponded to 90% of the tensile strength of Ti–6Al–4V. The extent of deformation of Ti–6Al–4V in the vicinity of the bonding interface was small compared with that of solid diffusion bonding because of the low bonding pressure. The bonding layer had an acicular microstructure which was composed of Ti₂Cu and α titanium with dissolved zirconium. Brittle products such as (Ti, Zr )₅ Si₃ or (Ti, Zr )₅ Si₄ were formed at the interface between the SiC fibres and the filler metal. These products existed only at the end of fibres, in very small amounts, therefore joint strength was not significantly affected by the products.

MST/1989     

Laser bonding and characterization of Kapton? FN/Ti and Teflon? FEP/Ti systems

Kapton^? FN and Teflon^? FEP (fluorinated ethylene propylene) polymers are resistant to most chemical solvents, heat sealable, and have low moisture uptake, which make them attractive as packaging materials for electronics and implantable devices. Kapton^? FN/Ti and Teflon^? FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Laser-bonded samples were tested with a micro-testing machine under lap shear load and the bond strength was determined. The bond strength for the Kapton^? FN/Ti and Teflon^? FEP/Ti systems was found to be 3.32 and 8.48 N/mm², respectively. The failure mode of the mechanically tested samples was studied by using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Chemical interactions during laser bonding of Kapton^? FN to titanium were studied by using X-ray photoelectron spectroscopy (XPS). The XPS results give evidence for the formation of Ti–F bonds in the interfacial region.     

Empfehlungen zur Werkstoffauswahl und zu den Schweißdaten für NH3-Lagerbehälter und NH3-Kesselwagen

Recommendations for Selection of Material and welding Electrodes for NH₃-storage Vessel and NH₃-Transport Container In liquid ammonia mostly only weld seams show cracks. Extensive SEM-investigations have shown that these are hydrogen induced cracks. During weld tests with the base materials St E 335 and St E 460 in different charges high yield strengths were determined in the weld material. Very often the yield strength values increase after stress relieving. This is caused by precipitation, which leads to a bracing of the lattice, thus raising the yield point. To ensure one of the base material adapted yield strength in the weld it is only possible in very rare cases with suitable weld additives. In the St E 460 with nitrogen and vanadium the yield strength value in the weld is even by use of the wire S 1 and neutral powder over 600 N/mm². It was found out that hydrogen induced cracks in the weld above 550 N/mm² yield strength occur very likely below 550 N/mm² occur very little. In the base material St E 355 the yield strength was limited for this reason in the weld with 500 N/mm² in the base material St E 460 limited with 550 N/mm². Proof has to be furnished for all welding procedures, sheet charges and weld additives applicable by means of welding probes.     

Reactions of Hf-Ag and Zr-Ag alloys with Al2O3 at elevated temperatures

We are studying reactions of Ti, V, Zr, and Hf with ceramics as part of a program to understand fundamental reaction and bonding mechanisms in active metal brazing of ceramics. In this paper we present results of experiments with model systems comprising Ag alloys that contain different amounts of Hf or Zr that were reacted with sapphire or 99.6% alumina for different times and temperatures in a controlled atmosphere furnace. In these alloys the Ag functions as an inert solvent, which allowed us systematically to determine the effects of changes in concentration of the active element. We observed qualitative wetting and spreading tendencies of the alloys during heating and examined cross sections after cooling using electron analytical techniques. For all reaction times studied, the Hf/Ag alloys formed a discontinuous reaction layer, which was consistent with earlier high-resolution electron microscopy that showed sub-micrometer HfO₂ particles embedded in the surfaces of the Al₂O₃ grains. By contrast, initial reaction of the Zr/Ag alloys with Al₂O₃ produced a continuous interface layer. With longer reaction times, the ZrO₂ reaction product became much thicker and exhibited three distinct zones at the interface. The results suggest that the rate limiting step in the Zr/Ag reaction is the chemical reaction at the interface, whereas with Hf/Ag reaction diffusion of products away from the interface is rate limiting.     

Les intercalaires Ax Ti S2 et Ax Zr S2. Structure et liaisons. (A = Li,Na, K,Rb, Cs)

A general survey of alkali metals intercalation compounds with titanium and zirconium disulfides is given. A model A⁺_x (Ti S₂^x? or A⁺ (Zr S₂)^x? with an electronic delocalization in the (Ti²S₂) or (Zr S₂) slabs, is suggested according to crystallographic and magnetic studies, N.M.R. measurements, and chemical behaviour. The alkali metal coordination is related to several factors: size of the A⁺ ion, value of the x parameter, strength of the T.S. bonds.     

Effects of hydroxyapatite/Zr and bioglass/Zr coatings on morphology and corrosion behaviour of Rex-734 alloy

To improve corrosion resistance of metallic implant surfaces, Rex-734 alloy was coated with two different bio-ceramics; single-Hydroxyapatite (HA), double-HA/Zirconia(Zr) and double-Bioglass (BG)/Zr by using sol–gel method. Porous surface morphologies at low crack density were obtained after coating and sintering processes. Corrosion characteristics of coatings were determined by Open circuit potential and Potentiodynamic polarization measurements during corrosion tests. Hardness and adhesion strength of coating layers were measured and their surface morphologies before and after corrosion were characterized by scanning electron microscope (SEM), XRD and EDX. Through the SEM analysis, it was observed that corrosion caused degradation and sphere-like formations appeared with dimples on the coated surfaces. The coated substrates that exhibit high crack density, the corrosion was more effective by disturbing and transmitting through the coating layer, produced CrO₃ and Cr₃O₈ oxide formation. It was found that the addition of Zr provided an increase in adhesion strength and corrosion resistance of the coatings. However, BG/Zr coatings had lower adhesion strength than the HA/Zr coatings, but showed higher corrosion resistance.     

Effects of hot pressing temperature on microstructure,hardness and corrosion resistance of Al2NbTi3V2Zr high-entropy alloy

A novel lightweight high-entropy alloy Al₂NbTi₃V₂Zr was fabricated by vacuum hot pressing. The effects of sintering temperature (1200–1550°C) on the microstructure, hardness and corrosion resistance of the alloy were investigated. Results showed that Al₂NbTi₃V₂Zr mainly consisted of simple cubic matrix and (Zr, Al)-based intermetallic phase (α-phase) at sintering temperatures of 1200–1350°C. Moreover, the matrix phase transformed from simple cubic to body-centred cubic phase, and (Ti, Zr, Al)-based intermetallic precipitated from the matrix at temperature of 1450°C. The fabricated Al₂NbTi₃V₂Zr alloy had low density of 5.05–5.23?g?cm^–3, high hardness of 510–728?HV and excellent corrosion resistance in 10?wt-% HNO₃ solution.     

Interfacial microstructure and strength of diffusion brazed joint between Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiC and 9Cr1MoV steel

Joining of composite, Al₂O₃-TiC, with heat-resistant 9Cr1MoV steel, was carried out by diffusion brazing technology, using a combination of Ti, Cu and Ti as multi-interlayer. The interfacial strength was measured by shear testing and the result was explained by the fracture morphology. Microstructural characterization of the Al₂O₃-TiC/9Cr1MoV joint was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy-dispersion spectroscopy (EDS). The results indicate that a Al₂O₃-TiC/9Cr1MoV joint with a shear strength of 122 MPa can be obtained by controlling heating temperature at 1130°C for 60 min with a pressure of 12 MPa. Multi-interlayer Ti/Cu/Ti was fused fully and diffusion occurred to produce interfacial layer between Al₂O₃-TiC and 9Cr1MoV steel. The total thickness of the interfacial layer is about 100 μm and Ti₃AlC₂, TiC, Cu and Fe₂Ti are found to occur in the interface layer.     

The characteristics of (Pb,La)(Zr,Sn,Ti)O<Subscript>3</Subscript> ceramics synthesized by coprecipitation method compared to conventional mixed oxide method

The relaxor antiferroelectric (Pb,La)(Zr,Sn,Ti)O₃ powders were synthesized by conventional mixed oxide method and coprecipitation method. The XRD patterns show that pure perovskite phase formation temperature was 700 °C for the coprecipitation method and that was 1,100 °C for the conventional mixed oxide method. Effect of the methods on sintering behavior and microstructures of the ceramics has been investigated by SEM. Both the samples exhibit typical antiferroelectric double hysteresis loops with maximum polarization of 18.2 μC/cm², forward-switching field of 6.2 kV/mm by conventional mixed oxide method, and 33.1 μC/cm², 4.3 kV/mm by coprecipitation method, respectively.     

Synthesis of High-Phase Purity SrTi1–xZrxO3 Ceramics by Sol-Spray Pyrolysis Method

SrTi₁–_xZr_xO₃ (0 ≤ x ≤ 1.0) ceramics were synthesized from powders generated by sol-spray pyrolysis. Crystal symmetry, morphology, and the band gap of the prepared ceramics were investigated as a function of Ti/Zr ratio. Substitution of Zr⁴⁺ for Ti⁴⁺ in the solid solution markedly effects crystal symmetry and grain growth and results in an increased band gap. Single-phase products with good crystallinity and dense microstructure were obtained after sintering at 1250°C.     

Spannungsrißkorrosion in hochreinem Wasser von 3–3 ½% NiCrMoV-Vergütungsstählen für Dampfturbinen-Scheiben und -Wellen. Teil I

SCC in High Parity Water In recent years intergranular stress corrosion cracking has occured world-wide in the shrink-fitted discs of low pressure turbine rotors made of low alloy steels. Only in a few cases steam impurities such as NaOH, Na₂CO₃, Na₂SO₄, H₂S or Nacl, which initiate SCC, could be found. To clarify the SCC-behaviour experiments on turbine disc steels with different chemical compositions an yield strength were performed in high purity water. The results show, that chemical composition has no effect on the crack initiation. Under high purity water conditions no crack initiation due to stress corrosion cracking is observed on the steel with a yield strength of 850 N/mm². On the steel with a yield strength of 1250 N/mm² which is not used in service, crack initiation occurs in pure water. But if sharp cracks already exist, crack propagation occurs in both cases. The investigations showed, that stress corrosion cracking of turbine discs can be prevented by a good water chemistry with a cation conductivity less than 0.2 μS/cm (μmho/cm).     

Schwingungsrißkorrosionsverhalten des Duplexstahles X 2 CrNiMoN 22 5 3 unter definierten Wärmeübergangsbedingungen

Corrosion fatigue behaviour of duplex stainless steel X 2 CrNiMoN 22 5 3 under heat transfer conditions The corrosion behaviour of metallic components is not only affected by the temperature of the corrosive environment but also by the heat transfer conditions between the heated material and the cooling agent. Therefore the corrosion fatigue behaviour of the austenitic-ferritic stainless steel X 2 CrNiMoN 22 5 3 (german material-number 1.4462) in 3% NaCl-solution is investigated for isothermal conditions and three different heat transfer conditions. The specimens are tested under cyclic tension load (R = s?_u/s?_o = 0) with a frequency off =25 Hz up to N_Grenz 10⁷. The isothermal fatigue strengths are 380 N/mm² for room temperature and 340 N/mm² for a temperature of 70°C. For heat transfer conditions between the sinusoidal loaded specimens and the corrosive agent a new developed testing equipment is presented. The corrosion fatigue strength for a heat flux of 45 KW/m² reaches a value of 410 N/mm², while the improvement relative to the isothermal room temperature strength is lower for higher heat flux values (100 and 150 KW/m²). The better corrosion fatigue behaviour for heat transfer conditions bases on the favourable conditions for the formation of the passive layer. The thickness of the layer is nearly twice as high as for isothermal room temperature corrosion and therefore the crack initiation is delayed. For higher values of heat flux local corrosion attack is found. With that the positive effect on corrosion fatigue strength is diminished.     

The solid state bonding of nickel,chromium and nichrome sheets to α-Al2O3

This paper describes experiments to measure the interfacial shear strengths of bonds formed between nickel, chromium and nichrome sheets hot pressed on to -Al₂O₃ single crystal plaques. Nickel developed bonds of 8×10³ psi (56 MN. m^–2) in shear when pressing was carried out under non-reducing conditions at 1100° C, 1 tsi (15 MN. m^–2) for 2 h: in the case of chromium, the effect of pressing temperature (1000 to 1300° C) pressing pressure (1/2 to 3 tsi [7.7 to 45 MN. m^–2]) and pressing time (1/2 to 7 h) on the bond was investigated. Nickel-chrome alloys produced from alternate nickel and chromium strips showed bond strengths up to 20×10³ psi (140 MN. m^–2) whilst commercial nickel-chrome (containing a silicon impurity) was not as effective in bonding to alumina. In material prepared from alternate strips of nickel and chromium, the degree of alloy homogenisation was investigated using microprobe analysis and suggestions made as to the mechanism of the interfacial reactions with alumina.     

Development of Al3Ti and Al3Zr intermetallic particulate reinforced aluminum alloy AA6061 in situ composites using friction stir processing

Aluminum rich intermetallic particles are potential reinforcements for discontinuously reinforced aluminum matrix composites (DRAMCs). The objective of the present work is to produce AA6061/Al₃Ti and AA6061/Al₃Zr composites using in situ casting technique and applying friction stir processing (FSP) to enhance the distribution and morphology of Al₃Ti and Al₃Zr particles. AA6061/Al₃Ti and AA6061/Al₃Zr DRAMCs were produced by the in situ reaction of inorganic salts K₂TiF₆ and K₂ZrF₆ with molten aluminum. The microstructure was observed using optical and scanning electron microscopy. AA6061/Al₃Ti DRAMC exhibited clusters of Al₃Ti particles while the segregation of needle shape Al₃Zr particles was observed in AA6061/Al₃Zr DRAMC. The prepared composites were subjected to FSP. Significant changes in the distribution and morphology of Al₃Ti and Al₃Zr particles were observed after FSP. The changes in microhardness and sliding wear behavior of AA6061/Al₃Ti and AA6061/Al₃Zr DRAMCs before and after FSP is detailed in this paper.     

Enhanced ferro- and piezoelectric properties in (100)-textured Nb-doped Pb(ZrxTi1 − x)O3 films with compositions at morphotropic phase boundary

To develop high-performance piezoelectric films on conventional Pt(111)/Ti/SiO₂/Si(100) substrates, sol-gel-derived highly [100]-textured Nb-doped Pb(Zr_xTi_1 − x)O₃ (PNZT) thin films with different Zr/Ti ratios ranging from 20/80 to 80/20 were prepared and characterized. The phase structure, ferroelectric and piezoelectric properties of the PZNT films were investigated as a function of Zr/Ti ratios, and it was confirmed that there was distinct phase transition of the PNZT system from tetragonal to rhombohedral when the Zr/Ti ratio varied across the morphotropic phase boundary (MPB). The Nb-doped PZT films showed enhanced remanent polarization but reduced coercive field, whose best values reached 75 μC/cm² and 82 kV/cm, respectively at the composition close to MPB. In addition, the [100]-textured PNZT film at MPB also shows a high piezoelectric coefficient up to 161 pm/V. All these properties are superior to those for undoped PZT films.