Evolution of interface microstructure and strength properties in titanium – stainless steel diffusion bonded transition joints

Abstract

Diffusion bonding was carried out to produce transition joints between commercially pure titanium and 304 stainless steel at a temperature of 800°C for different times ranging from 30 to 180 min. in steps of 30 min under load in vacuum. The diffusion couples thus produced were studied using optical microscopy, scanning electron microscopy, and electron probe microanalysis to characterise the reaction layers formed in the diffusion zone. The chemical compositions of these layers indicate that intermetallics like σ phase, Fe₂ Ti, Cr₂ Ti, χ phase, FeTi, β-Ti, and Fe₂ Ti₄ O are formed in the reaction zone. The presence of these intermetallic compounds was also confirmed by the X-ray diffraction technique. Maximum bond strength of ~242 MPa was obtained for diffusion welded joints processed for 120 min. At this joining time, the plastic collapse of the surface asperities reaches near completion, favouring the interdiffusion of chemical species. Reduction in the bond strength of the transition joint processed for 180 min is due to the formation of a large volume fraction of voids in the reaction zone. Under tensile loading, failure takes place through α-Fe + χ phase mixture for transition joints processed in the time range of 30 – 90 min and through β titanium for joining times greater than 120 min.     

43—THE INTRODUCTION OF AMIDE AND ESTER CROSS-LINKS INTO WOOL

An account is given of the examination of carbodiimides and ethyl chloroformate as cross-linking agents for wool. The level of cross-linking was estimated from the extent of swelling of the treated wool in formic acid. Carbodiimide treatments resulted in the condensation of amino and carboxyl side chains to give amide cross-links; ester cross-links were also formed by condensation of hydroxyl and carboxyl side chains, Hydroxylamine treatments, which cleaved the ester but not the amide cross-links, were used to estimate the relative abundance of the two types of cross-link. N-Hydroxysuccinimide strongly promoted the cross-linking of wool with carbodiimides, most of the extra cross-links introduced being esters.

The treatment of wool with ethyl chloroformate introduced relatively few cross-links. The main reactions are believed, on the basis of indirect evidence, to be esterification of carboxyl side chains and conversion of amino side chains to urethanes.     

Zinc compounds as flame retardants and smoke suppressants for rigid PVC

Abstract

The effect of the concentration of zinc hydroxy-stannate and zinc borate on the fire performance of rigid PVC formulations has been investigated. Fire testing was carried out using cone calorimetry as well as the limiting oxygen index (LOI) test. In addition, further testing was done to check that incorporation of the fire retardant additives did not have any detrimental effects on other properties of the formulated PVC, such as heat stability, colour or impact strength. The results demonstrated that zinc hydroxy-stannate is an excellent fire retardant and smoke suppressant at additions levels of 3 parts per hundred parts of PVC. Zinc borate did not have the excellent fire retardant properties of zinc hydroxy-stannate, but was found to be an efficient and cost-effective smoke suppressant, although the presence of free zinc oxide in the sample affected the thermal stability of the formulation.     

12—A CRITIQUE OF SOME HYPOTHESES RELATING TO THE HETEROGENEITY OF THE HIGH-SULPHUR PROTEINS OF WOOL

Joubert and Burns prepared a large number of fractions from the high-sulphur proteins of wool and estimated their molecular weights and amino-acid compositions. Their data have been re-examined in order to look for statistically significant interrelations between amino acids and between the proportion of various amino acids and molecular weight. Statistical analysis of the data is also used to examine the credibility of some hypotheses concerning the mechanism of keratin biosynthesis and to provide further evidence for the existence of families of proteins within the high-sulphur fractions of wool.     

35—THE SETTING OF WOOL: ENHANCEMENT BY THE INTRODUCTION OF BULKY GROUPS

An account is given of the setting behaviour of wool fabrics after treatment with a variety of anhydrides of carboxylic acids. The incorporation of relatively large numbers of small acyl groups had little effect on the settability, but bulky acyl groups caused a large enhancement. Unlike untreated wool, wool containing large numbers of bulky acyl, e.g., benzoyl, groups can be steam-set extremely readily without any need for prior wetting.

From a detailed study of the setting behaviour and set stability of benzoylated fabric, it was concluded that two main types of interaction were involved, namely, electrostatic and hydrophobic interactions. Electrostatic interactions were believed to predominate at low levels of acylation, the result being inhibition of set. These were outweighed by hydrophobic interactions at higher levels of acylation with bulky anhydrides, which resulted in set stabilization. Disulphide-bond rearrangements appear to play little part in the setting of wools with high contents of bulky acyl groups.     

5—THE CONSTITUTION OF THE EPICUTICLE OF WOOL

Epicuticle, isolated from wool via the Allwörden reaction, was examined by electron microscopy and analysed chemically. It is proteinaceous; lipids and carbohydrates could not be detected. The component amino acids are: cystine, glycine, glutamic acid, serine, valine, alanine, lysine, α-amino-adipic acid, and threonine. A tentative model for the epicuticle is proposed.     

Rubber-to-metal bonding by silanes

This paper deals with the bonding of sulfur-vulcanized rubber compounds to metals. It had previously been reported that bis-(triethoxysilyl)ethane and vinyltriethoxysilane were found to work for bonding peroxide-cured rubber compounds to metals. These silanes were found not to work with sulfur-cured rubber compounds. In this case, a mixture of bis-(trimethoxysilylpropyl)amine and bis-(triethoxysilylpropyl) tetrasulfide was found to work and results are presented of experiments in which brass, steel, and electrogalvanized steel were bonded to a typical tire cord skim compound with and without a cobalt additive. This new silane treatment was found to be as effective as or better than brass adhesion to cobalt-containing rubber compounds. The superior corrosion protection offered by the silanes was also demonstrated using DC corrosion and polarization resistance measurements. The silane process reported in this paper behaves almost similarly with all metal substrates. In this paper, the structure of the silane film on a metal substrate is studied and a model is proposed for a possible mechanism of the adhesion of rubber compounds with silane-coated metals.     

34—A STUDY OF WOOL KERATIN BY ELECTRON-SPIN-RESONANCE SPECTROSCOPY

An account is given of the study by means of electron-spin-resonance spectroscopy of free radicals induced in wool and chemically modified wool by X-rays. ‘Cystine’ radicals are shown to be formed by only a portion of the total number of residues present, and these are associated with amino end-groups. Spectral changes produced by chemical modification of the cystine are explained in terms of superimposed singlet, doublet, and quartet absorptions, and it is proposed that the quartet absorptions originate from free radicals on the alanine side chains. It is shown that X-irradiation in air modifies the wool structure so that previously ‘inert’ disulphide links are capable of radical formation.     

Study of heat of reaction between plasma-polymer-coated silica fillers and biphenyl epoxy resin

Silica fillers were coated by plasma polymer coatings of 1,3-diaminopropane, allylamine, pyrrole, 1,2-epoxy-5-hexene, allyl mercaptan and allyl alcohol using RF plasma (13.56 MHz). The coated fillers were then mixed with biphenyl epoxy, phenol novolac (curing agent) and/or triphenylphosphine (catalyst), and subjected to DSC analyses in order to elucidate the chemical reaction between functional moieties in the plasma polymer coatings and the epoxy resin. For comparison, samples were also prepared with liquid monomers, biphenyl epoxy, phenol novolac and/or triphenylphosphine. In addition, silicon wafers were coated by plasma polymerization and analyzed by FT-IR. Only the samples with 1,3-diaminopropane and allylamine plasma-polymer-coated silica fillers showed heat of reaction peaks when they were mixed with biphenyl epoxy resin, while these samples as well as the sample with pyrrole plasma-polymer-coated silica fillers exhibited heat of reaction peaks when mixed with both biphenyl epoxy and phenol novolac (curing agent). However, all plasma polymer samples exhibited heat of reaction peaks when they were mixed with biphenyl epoxy, phenol novolac and triphenylphosphine. The samples with liquid monomers showed a similar behavior, but the peaks appeared in the lower temperature range.