Crevice and under deposit corrosion resistance of titanium alloys in highly aggressive environments

The outstanding resistance of titanium to corrosion in a wide range of aggressive conditions has been confirmed by successful applications in the chemical and process industry, (CPI), over many years. Crevice and underdeposit corrosion threshold temperatures frequently set the limits for wider application. Research to extend the capabilities of titanium and its alloys in extremes of temperature, stress and corrosion has pursued two objectives: 1. To reduce the cost of enhanced crevice corrosion resistance using palladium. 2. To provide higher strength alloys with improved crevice corrosion resistance. The first section of this paper details the range of enhanced corrosion resistance alloys containing nominally 0.05 % palladium, (ASTM Grades 16 and 17); and the measures taken to confirm that the homogeneity of composition is achieved in standard 4500 kilo ingots, now being melted for production of a full range of mill products. The second section covers the assessment and modification of alloys and the development of new alloys for specific performance goals under high stress in hostile environments. Applications are described in the offshore oil and gas extraction, desalination plant and equipment and flue gas desulphurisation plant. Reference is made to the challenges presented by emerging technologies for the safe disposal by wet oxidation of toxic substances and process effluents.     

Morphological studies of some high nickel alloys in the region of the breakdown of passivity

The corrosion morphologies of four important high nickel alloys, Hastelloy B, Monel 400, Hastelloy C and Inconel 611 in a neutral (pH = 8.3) chloride/bicarbonate medium polarized potentiostatically until an anodic current density of 0.30 mA cm⁻² was reached have been studied.It has been shown that Hastelloy B undergoes shallow pitting; Monel 400 produces a porous film with dissolution sites followed by pits covered with corrosion products; Hastelloy C undergoes intergranular corrosion and Inconel 611 undergoes catastrophic pitting. The most superior alloy of these is Hastelloy C.     

Morphological studies of some high nickel alloys in the region of the breakdown of passivity

The corrosion morphologies of four important high nickel alloys, Hastelloy B, Monel 400, Hastelloy C and Inconel 611 in a neutral (pH = 8.3) chloride/bicarbonate medium polarized potentiostatically until an anodic current density of 0.30 mA cm^?2 was reached have been studied.It has been shown that Hastelloy B undergoes shallow pitting; Monel 400 produces a porous film with dissolution sites followed by pits covered with corrosion products; Hastelloy C undergoes intergranular corrosion and Inconel 611 undergoes catastrophic pitting. The most superior alloy of these is Hastelloy C.     

Modeling the hydrogen-induced cracking of titanium alloys in nuclear waste repository environments

This article considers hydrogen-induced cracking of titanium grade 7 and other relevant titanium alloys in the current waste package design for the environmental conditions anticipated within the proposed Yucca Mountain nuclear waste repository in Nevada. In particular, corrosion processes possible in the aqueous environments expected within this site are considered, including key corrosion processes that could occur and the expected corrosion performance of these alloys. It can be concluded that, based on the conservative modeling approaches adopted, hydrogen-induced cracking of titanium alloys will not occur under nuclear waste repository conditions since there will not be sufficient hydrogen in the alloy even after 10,000 years of emplacement. For more information, contact Fred Hua, Bechtel SAIC Company, LLC, 1180 Town Center Drive, Las Vegas, NV 89144; e-mail Fred_Hua@ymp.gov.     

Anodic passivity of glassy Ni83B17 alloy in sulphuric acid

The anodic passivation of Ni₈₃B₁₇ glassy was investigated in sulphuric acid solutions with respect to the degree of proton hydration and the structure of acid. The possibility of passivation in methanolic solutions of sulphuric acid was also examined. The investigations involved electrochemical measurements, XPS and sulphur dioxide analyses. When acid concentration is low, the passivity of Ni₈₃B₁₇ is a result of the formation of an oxide layer in the presence of “free” water molecules (i.e. not bound to protons). In concentrated sulphuric acid, the passivation may occur as a result of the oxidative ability of acid connected with S⁶⁺ ion reduction. At intermediate acid concentrations a mixed salt-oxide layer is formed. The passivity of Ni₈₃B₁₇ was also observed in methanolic solutions of sulphuric acid, as a result of the oxidising ability of the acid.     

Characteristics of passivity of extremely corrosion-resistant amorphous iron alloys

The amorphous FeCrPC alloy was compared with the crystallized alloy having the same composition in potentiodynamic polarization curves and with an 18Cr8Ni stainless steel in current decay after abrading the specimens under anodic polarization. Through these results along with the previous ESCA study, the extremely high corrosion-rseistance of the amorphous iron alloys containing 8 at.% or more chromium has been interpreted in terms of the rapid formation of thick, uniform, highly corrosion-resistant passive film due to the characteristics of the amorphous alloys.     

钛及钛合金的焊接

钛及钛合金因其优异的综合性能和独特功能被广泛应用于航空航天和海洋工程等重要领域,而不同类型的钛及钛合金的性能各不相同。介绍钛及钛合金的分类及其焊接特性,分别描述工业纯钛、α型钛合金、α+β型钛合金、近β和β型钛合金的分类方法、添加元素及基本特性,综述不同类型的钛及钛合金的国内外焊接研究现状,重点关注各种钛及钛合金的焊接方法、焊后组织和性能,归纳总结各种钛及钛合金的主要焊接方法为TIG焊、激光焊和电子束焊。     

Anodic oxidation of Ta/Fe alloys

The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm V⁻¹. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface.     

Ternary alloys of titanium

The results of a preliminary study of 113 ternary titanium-base alloys are described. The compositions investigated were as follows:

1. 1.
   Ternary titanium-carbon alloys containing copper, silicon, vanadium, chromium, manganese, iron, or cobalt.
    
2. 2.
   Ternary titanium-nitrogen alloys containing chromium.
    
3. 3.
   Ternary titanium-chromium alloys containing additions of vanadium, molybdenum, tungsten, cobalt, or nickel.
    
4. 4.
   Ternary titanium-manganese alloys containing additions of silicon, chromium, tungsten, or iron.
    

Tensile properties, minimum bend radii, hardnesses, response to heat treatment and aging treatment, and phase relationships for these alloys were determined.     

Nitriding of titanium alloys

Conclusions Nitriding at pressures from 300 to 10^–2 mm Hg with the nitrogen inflow cut off and holding at low pressure is the best method of obtaining a case of substantial depth, with satisfactory mechanical properties of the base metal.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 72–74, June, 1973.     

Inclusions in melting process of titanium and titanium alloys

This paper summarizes melting methods of titanium and titanium alloy, such as vacuum arc melting(VAR) and electron beam cold hearth melting(EBCHM), and the related inclusions formed when using these melting methods. Low-density inclusions are resulted from contamination of air, and high-density inclusions are caused by refractory elements. The formation process of inclusions was analysed. The removal mechanism of different kinds of inclusions was specified. Low-density inclusions are removed mainly by resolving. This is a comprehensive process containing reaction diffusion. The resolving rate of high-density inclusions is so low that these inclusions are mainly removed by sedimentation. The experiments and physical models of inclusions are detailed. In various melting methods, vacuum arc melting is prominent. However, this method cannot remove inclusions effectively, which usually results in repeat melting. Electron beam cold hearth melting has the best ability of removing inclusions. These results can provide instructions to researchers of titanium and titanium alloys.     

Anodic oxidation and dielectric behaviour of aluminium-niobium alloys

The anodizing behaviour of sputtering-deposited Al-Nb alloys, containing 21, 31 and 44 at.% niobium, has been examined in 0.1 M ammonium pentaborate electrolyte with interest in the composition and the dielectric properties of the anodic oxides. RBS and TEM revealed amorphous oxides, containing units of Nb₂O₅ and Al₂O₃ in proportion to the alloy composition. Xenon marker experiments indicated their growth through migration of the Nb⁵⁺, Al³⁺ and O²⁻ species, with cation transport numbers, in the range 0.31-0.35, and formation ratios, in the range 1.35-1.64 nm V⁻¹, intermediate between those of anodic alumina and anodic niobia. Al³⁺ ions migrate slightly faster than Nb⁵⁺ ions, promoting a thin alumina layer at the film surface, although this layer is penetrated by fingers of the underlying niobium-containing oxide of relatively reduced ionic resistivity. The incorporation of units of Nb₂O₅ into anodic alumina increases the dielectric constant from about 9 to the range 11-22 for the investigated alloys.     

Anodic oxidation of Al–Ag alloys

The anodic oxidation of solution-treated and quenched Al–Ag alloys containing 0.3, 0.6, 0.9 and 1.2 at.%Ag, is examined in ammonium pentaborate electrolyte, which leads to growth of barrier-type anodic films. Enrichments of silver, 3.1×10¹⁵ Ag atoms cm⁻², are developed in the alloys immediately beneath the amorphous alumina films, with the level of enrichment not depending significantly upon the composition of the bulk alloy. The enrichment is relatively low due to clustering of silver atoms in the bulk alloy, which reduces the concentration of silver that is available to enrich from solid solution. Silver species are incorporated into the anodic film, where they migrate outward faster than Al³⁺ ions.