The “C” family of Ni-Cr-Mo alloys' partnership with the chemical process industry: The last 70 years

The “C” family of alloys, the original being Hastelloy® alloy C (1930's) was an innovative optimization of NiCr alloys having good resistance to oxidizing corrosive media and NiMo alloys with superior resistance to reducing corrosive media. This combination resulted in the most versatile corrosion resistant alloy in the “NiCrMo” alloy family, with exceptional corrosion resistance in a wide variety of severe corrosive environments typically encountered in CPI and other industries. The alloy also exhibited excellent resistance to pitting and crevice corrosion attack in low pH, high chloride oxidizing environments and had virtual immunity to chloride stress corrosion cracking. These properties allowed this alloy to serve the industrial needs for many years, although it had some limitations. The decades of the 1960's (alloy C-276), 1970's (alloy C-4), 1980's (alloy C-22 and 622) and 1990's (alloy 59, alloy 686 and alloy C-2000) saw newer alloy developments with improvements in corrosion resistance, which not only overcame the limitations of alloy C, but further expanded the horizons of applications as the needs of the CPI became more critical, severe and demanding. Today the originally alloy “C” of the 1930's is practically obsolete except for some usage in form of castings. This paper presents a chronology of the various corrosion resistant alloy developments during this century, with special emphasis on the last 70 years evolution in the “C” family of NiCrMo alloys and their applications.     

Oxidation and Creep Limited Lifetime of Kanthal APMT®, a Dispersion Strengthened FeCrAlMo Alloy Designed for Strength and Oxidation Resistance at High Temperatures

Kanthal APMT^® is an FeCrAlMo alloy optimized for continuous service up to 1,250 °C (~2,300 °F). Rapid solidification powder metallurgy applied on this FeCrAlMo composition provided an oxide dispersion strengthened microstructure. The alloy exhibits an attractive combination of resistance to oxidation and corrosion and excellent form stability. In this study, oxidation and corrosion properties were investigated, as well as mechanical properties at elevated temperature. It was shown that an adherent alumina layer on the alloy surface formed during service that provided excellent resistance to corrosion attacks in most industrial atmospheres and gave great advantages compared to chromia forming high temperature Ni-base alloys in terms of maximum operating temperature and life. Focus was set on oxidation and creep properties but also other important aspects are discussed.     

The hydrogen embrittlement of titanium-based alloys

Titanium-based alloys provide an excellent combination of a high strength/weight ratio and good corrosion behavior, which makes these alloys among the most important advanced materials for a variety of aerospace, marine, industrial, and commercial applications. Although titanium is considered to be reasonably resistant to chemical attack, severe problems can arise when titanium-based alloys come in contact with hydrogen-containing environments, where they can pick up large amounts of hydrogen, especially at elevated temperatures. The severity and the extent of the hydrogen interaction with titanium-based alloys are directly related to the microstructure and composition of the titanium alloys. This paper addresses the hydrogen embrittlement of titanium-based alloys. The hydrogen-titanium interaction is reviewed, including the solubility of hydrogen in α and β phases of titanium and hydride formation. Also, the paper summarizes the detrimental effects of hydrogen in different titanium alloys. For more information, contact Dan Eliezer, Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel; +972-7-646-1467; fax +972-7-646-1475; e-mail deliezer@bgumail.bgu.ac.il.     

W-Ni-Cu 和W-Ni-Fe合金的腐蚀性能

高比重钨合金是一种具有高密度,高机械强度和良好的耐腐蚀性等特性的复合材料,并广泛应用于工业和军事中。本文采用沉浸实验和电化学实验对两种钨合金(90％W-6％Ni-4％Cu和95％W-3.5％Ni-1.5％Fe)的腐蚀性能进行了研究。结果的表明,当W-Ni-Cu合金发生电偶腐蚀时,W相首先遭到腐蚀,而在W-Ni-Fe合金中,粘结相会先发生腐蚀。电动位极化测量结果表明pH值对高比重合金钨合金腐蚀速率有显著影响,与酸性环境相比较,合金在中性溶液中得到较低的腐蚀速率。根据SEM和EDX的结果分析了合金成分的溶解以及腐蚀产物的生成等腐蚀机理。     

Environmental behavior of beta titanium alloys

Stemming from their unique combination of elevated strength, low density, and good overall corrosion resistance, beta titanium alloys have become attractive candidate materials for critical, high-stress components in corrosive services. An overview of the comparative corrosion resistance of beta alloys to conventional alpha and alpha/beta titanium alloys in common industrial and aerospace service environments generally reveals attractive behavior depending on the environment and alloy composition and, in some cases, alloy condition. Expanded performance windows are especially noted for the molybdenum-rich beta alloys, particularly with regard to resisting reducing acids, stress corrosion, and high-temperature localized chloride attack, along with hydrogen and oxidation resistance. Where applicable, implications of this enhanced corrosion performance on current and perspective beta alloy applications are also noted.     

Ultrafine Particulate Dispersed High-Temperature Coatings by Hybrid Spray Process

Oxide dispersion strengthened alloys (ODS), although not commonly used in coating applications, have long been used for high-temperature structural applications due to their superior creep properties. In this paper, we present the design, synthesis, and characterization of a new class of functionally engineered high-temperature coatings in which ultrafine oxide particulates are dispersed in the matrix alloy to achieve superior creep resistance along with improved high-temperature corrosion and erosion resistance. These coatings were fabricated using a novel technique called “hybrid spray process”. Hybrid spray technique combines arc spray and high-velocity oxy fuel (HVOF) spray processes; the metallic matrix alloys are fused by the wire arcing component of the process, whereas the ultrafine particles are synthesized in-flight by the HVOF component from liquid precursors. These particulate dispersed high-temperature composite coatings were fabricated using liquid precursors for SiO₂, Cr₂O₃, Al₂O₃, and wire feed stock of 55/45 NiCr, in one step. The coatings were then characterized using electron microscopy (SEM/TEM) and thermogravimetric analysis (TGA). High-temperature erosion, oxidation, and corrosion performance of these coatings were also evaluated and compared with 304 stainless steel, arc sprayed NiCr coatings as well as Alloy 625 overlay cladding. The hybrid spray process produced dense coatings with uniform dispersion of the ultrafine oxide particles. Further, these coatings also demonstrated superior corrosion, erosion, and oxidation resistance; SiO₂ particulate dispersion being most effective in terms of high-temperature corrosion resistance.     

On the importance of a connected hard-phase skeleton for the creep resistance of Mg alloys

The low density of Mg alloys renders them attractive for lightweight constructions. However, creep resistance remains an important limitation of Mg alloys for, for example, automotive power train applications. To gain a more detailed understanding of the correlation between microstructure and creep properties in die-castable Mg alloys, AZ91 alloys with nominal additions of 0, 1, 3, and 5 mass% Ca and the commercial alloy MRI 230D have been investigated. Creep tests show an increase in creep strength with increasing Ca addition and increasing cooling rate. Scanning electron microscopy reveals that this is correlated with an increasing interconnectivity of the intermetallic phase skeleton (in addition to the effect of small precipitates within the α-Mg matrix found in the case of MRI 230D). A simple isostrain composite analysis illustrates that a more interconnected skeleton shields more load from the matrix. Precipitation hardening can additionally strengthen the matrix, and thus the combination of both design approaches results in the highest observed creep resistance.     

Al-Ti、Al-Ti-C中间合金对AZ91D镁合金组织和性能的影响

研究了Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金对AZ91D镁合金的组织、力学性能和耐腐蚀性能的影响。结果表明,添加Al-5Ti中间合金使晶粒粗化,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金使晶粒细化,Al-8Ti-2C中间舍金的细化效果明显且细化后组织细小均匀;添加Al-5Ti中间合金使合金的力学性能降低,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的拉伸强度和伸长率得到了提高;添加Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的耐腐蚀性能得到了改善。对于AZ91D合金而言,Al-8Ti-2C中间合金是一种良好的晶粒细化剂。     

Thermal stability and creep behavior of Ti–V–Cr burn-resistant alloys

The thermal stability and creep behavior of Ti–35V–15Cr (35V alloy) and Ti–25V–15Cr (25V alloy) burn-resistant titanium alloys are researched. The results show that post-exposure tensile properties deteriorated with the increase in exposure temperature (450–600 °C). The decrease in tensile properties of the 35V alloy results from the combination of surface oxidation and microstructural changes and the decrease in tensile properties of the 25V alloy results from surface oxidation. The main change of the microstructure during thermal exposure is the heterogeneous precipitation of α phase on β grain boundaries. Increased vanadium content in the alloy shows an adverse effect on alloys’ thermal stability. The creep resistance of the 35V alloy is little better that that of the 25V alloy. During creep exposure at 540 °C for 100 h, the heterogeneous precipitation of α phase on β grain boundaries in 35V alloy strengthens the grain boundary, leading to increases in the creep resistance, while the heterogeneous precipitation of α phase in grains and grain boundaries in the 25V alloy is rod-like, leading to decreases in the creep resistance.     

耐热铸造镁合金的研究现状及其发展趋势

耐热铸造镁合金在航空航天以及汽车工业等领域得到了广泛应用。本文主要介绍了Mg-Al系、Mg-Zn系和Mg—RE系耐热铸造镁合金的研究现状；对新型高性能耐热镁合金的发展趋势提出了一些见解，指出，合金化方法作为解决镁合金高温性能不足的最有效的手段之一，应该进一步通过优化合金元素组合，进行有效的合金设计，解决铸造镁合金在耐高温、抗蠕变等方面存在的问题。     

新型医用Ti-24Nb-4Zr-8Sn合金在Hanks溶液中的电化学腐蚀行为研究

采用极化曲线分析、电化学阻抗谱（EIS）测试和浸泡实验的方法,并结合XPS,XRD和SEM等分析手段对新型医用Ti-24Nb-4Zr-8Sn合金在37℃的Hanks人工模拟体液中的电化学腐蚀行为进行了研究,并与纯Ti和Ti-6Al-4V合金进行了比较.结果表明:在37℃的Hanks溶液中,Ti-24Nb-4Zr-8Sn合金的腐蚀电流密度与纯Ti相等,并且钝化性能优于纯Ti和Ti-6Al-4V,这与其钝化膜中存在大量的Nb₂O₅密切相关;EIS结果显示,Ti-24Nb-4Zr-8Sn合金表面形成内层致密而外层疏松的双层钝化膜结构,致密层特性对材料的耐蚀性能起到决定性作用;随着浸泡时间的延长,致密内层的电阻大幅度提高,Ti-24Nb-4Zr-8Sn合金的耐蚀性能增强,同时疏松外层中的微缺陷发展成为宏观裂纹,造成疏松外层整体脱落.     

Corrosion behaviour of alloy 31 – UNS N08031 – under conditions of oil & gas production

The corrosion behaviour of alloy 31 (UNS N08031‐31Ni – 27Cr – 6.5Mo – 1.2Cu – 0.2N – bal. Fe) was tested in laboratory and field tests in seawater with and without additions of CO₂ and/or H₂S in slow strain rate tests, and in SSC (Sulphide Stress Corrosion) tests according to NACE MR0175. The results demonstrate a high resistance of alloy 31 to localised corrosion. Due to the high chromium and molybdenum concentration, its resistance to pitting and crevice corrosion in chloride‐contaminated seawater is significantly higher than that of alloy 28 and alloy 825 and it equals that of typical nickel base alloys like alloy 625. Alloy 31 is not sensitive to chloride‐induced stress corrosion cracking, either with or without H₂S, or sulphide stress cracking. Alloy 31 is approved for sour gas applications up to LEVEL VI in NACE MR 0175. The combination of properties makes alloy 31 an attractive choice for components in oil and gas production including wirelines, umbilicals, tubing, piping and topside application.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals — in particular Pd — having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and, simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloy as to corrosion and creep resistance.     

Enhancing the intergranular corrosion resistance of high Mg-alloyed Al–Mg alloy by Y addition

Microalloying is thought to improve the performance of Al–Mg alloys commonly used in transport applications. The effect of Y addition (0–0.4%) on the microstructure, mechanical properties, and corrosion resistance of Al–9.2Mg–0.7Mn alloy is investigated for potential use in engineering applications. The generation of the β-Al₃Mg₂ phase along the grain boundaries is suppressed in the as-cast alloy due to the formation of the AlMgY ternary phase. The average intergranular corrosion mass loss of the alloy with 0.1% Y addition decreases about 53.1% almost at no expense of mechanical performance in the as-rolled alloy after annealing. Moreover, the alloy with 0.1% Y addition shows the corrosion mass loss about 30.2% lower than the Y-free alloy in the sensitized state. The enhanced corrosion resistance of the alloy can be ascribed to the reduced β-Al₃Mg₂ precipitation along the grain boundaries associated with Y addition.     

Einfluß von Chrom,Molybdän und Stickstoff auf die Korrosionsbeständigkeit des Ni-freien,austenitischen Edelstahles Macrofer 2515MoN (W.-Nr.: 1.4653)

Influence of chromium, molybdenum and nitrogen on the corrosion resistance of the Ni-free, austenitic stainless steel Macrofer 2515MoN (German Alloy No. 1.4653) Nitrogen alloyed, Ni-free, austenitic stainless steels comprising of more than 1 wt.-% nitrogen are a new group of alloys with promising properties. They show a very interesting combination of high strength and toughness with a high corrosion resistance. This combination of properties make the alloys not only suitable for fasteners but also for parts for medical and dental applications. This work shows the influence of chromium, molybdenum and nitrogen on the corrosion resistance of Fe25Mn-alloys in media typical for the above mentioned applications. According to these results Fe25Mn-alloys with appr. 20 wt.-% chromium, about 3 wt.-% molybdenum and appr. 1,3 wt.-% nitrogen have an excellent corrosion resistance in Ringer solution, artificial saliva and artificial sweat. The critical pitting temperature (CPT) as well as the critical crevice temperature (CCT) with 61°C respectively 37°C tested according ASTM G 48A provided significantly higher temperatures when compared to the commercially well established Ni-austenite X6CrNiMoTi17-12-2 (German Alloy No. 1.4571).     

Evolution of the impedance diagrams of 8090 Alloy in saline solution with low aggressiveness

Aircraft industry has focused in the search for new materials with high performance properties such as composite materials and aluminium alloys. During the last decade a new generation of aluminium-lithium alloys have been developed due to their low density and high elastic modulus. From corrosion viewpoint most of the work published on these alloys are based on atmospheric exposure tests and accelerated laboratory tests. Recently, an increasing interest has been paid in the use of electrochemical techniques on aluminium alloys due to their main advantages: determining of corrosion kinetics in real time and knowledge of the corrosion mechanism. This paper attempts to establish a correlation between the evolution of the impedance diagrams and the process of the attack undergone by a commercial 8090 T8171 alloy in sodium chloride solutions. During the first 100 h of immersion the electrochemical impedance spectroscopy reveals that the corrosion process is under charge transfer resistance control. After this time, the technique showed clearly the role of the adsorbed ions from the electrolyte, which promotes an intergranular attack on the alloy.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals – in particular Pd – having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloys as to corrosion and creep resistance.     

The oxidation performance of modern high-temperature alloys

The high-temperature oxidation resistance of an alloy is a key design criterion for components in a variety of industrial applications, such as advanced gas turbines, industrial heating, automotive, waste incineration, power generation and energy conversion, chemical and petrochemical processing, and metals and minerals processing. The importance of correctly assessing the long-term oxidation behavior of high-temperature alloys is illustrated. As applications move to higher temperatures, new alloys are needed. In this paper, the oxidation performance of three newly developed alloys, an alumina-forming Ni-Fe-Cr-Al alloy, a γ′-strengthened Ni-Cr-Co-Mo-(Al+Ti) alloy, and a nitride-strengthened Co-Cr-Fe-Ni-(Ti+Nb) alloy is presented. Author’s note: All compositions reported in this article are in weight percent.     

The effect of Mg alloy substrate on “electroless” E-coating performance

The corrosion performance of “electroless” E-coating pre-film on eight different Mg alloys is compared in a 5 wt.% NaCl. The results show that the alloys have different levels of surface alkalization effect, resulting in different thickness of films formed on the alloys. The alloying elements in a Mg alloy do not directly influence the film formation and corrosion performance. Instead, the corrosion resistance of substrate has a significant effect on the degradation or corrosion process of the coated Mg alloy. The corrosion resistance of the substrate Mg alloy can influence the porosity of pre-film during “electroless” E-coating deposition, and it is also a critical factor determining the film corrosion degradation.     

T6I6时效对6061铝合金拉伸及晶间腐蚀性能的影响

对T6I6时效处理的6061铝合金的拉伸性能、晶间腐蚀性能和电导率进行了测试,并采用OM和TEM对其组织进行了观察.结果表明,6061铝合金经180℃×8 h T6峰值时效后,虽然强度较高,但有严重晶间腐蚀倾向;T6I6预时效时间对拉伸性能影响不大,但中断时效温度和时间对其影响显著.由于较高的中断时效温度和较长的中断时间能获得高密度的晶内析出相和呈球状不连续分布的晶界析出相,因此,T6I6时效处理后的6061铝合金不仅能保持较高强度,同时还能显著提高晶间腐蚀抗力.经180℃×2 h+150℃×2160 h+180℃×8 h T6I6时效,合金抗拉强度和屈服强度分别为348.5和326.9 MPa,相对于T6状态,仅分别下降了2.1%和1.4%,腐蚀类型由T6状态的晶间腐蚀转变为均匀腐蚀,腐蚀深度约为30μm.