Cause Of Brittleness Research Articles

Plastic deformation of beta-Ti-Mo alloys with isothermal omega phase

Aging of metastable beta-Ti alloys leads to the precipitation of omega phase, resulting in a significant loss in ductility (omega brittleness). This presentation reports the results of 3D observations of isothermal omega phase by an orthogonal FIB/SEM system. It was revealed that the shape of omega phase particles varies with the particle size. By serial sectioning, it was possible to obtain a 3D image for the volume of several micrometer cube containing numerous omega particles. The volume fraction of omega phase was qualitatively determined. The value was much lower than the previous investigation by X-ray diffraction by Hickman in 1969. The SEM and TEM revealed the formation of shear bands in the cold rolled samples, where the shearing of omega phase and transformation into beta phase while maintaining the depletion of Mo was found. After the HPT deformation, white etching layers are formed near the median plane of the disc, where the omega phase particles were absent and exhibit significantly lower hardness values. These findings may help to clarify the cause of brittleness in beta Ti alloys with isothermal omega phase.

Ductility enhancement of autoclaved cellulose fiber reinforced cement boards manufactured using a laboratory method simulating the Hatschek process

Autoclaved fiber cement (FC) boards manufactured using the Hatschek process are commonly used as building products such as siding and shingles. Despite their advantages, these products may exhibit low ductility and volume instability. A common, yet expensive, method for improving ductility is increasing the fiber content. In this study, a procedure to manufacture FC boards in the laboratory was introduced, and alternative economical methods for increasing the boards’ ductility were investigated. Ductility was measured using a 3-point or 4-point bending tests, while the microstructure of the boards was studied using scanning electron microscopy. The results show that ductility of FC boards was improved by reducing their matrix tensile strength. This was achieved by reducing the density (increasing porosity) of FC boards or by partially replacing Portland cement with fly ash. Fiber mineralization was not found to be the cause of brittleness in the investigated FC boards.

Synthesis, Characterization and Cold Workability of Cast Copper-Magnesium-Tin Alloys

The use of Mg as an alloying element in copper alloys has largely been overlooked in scientific literature and technological applications. Its supposed tribological compatibility with iron makes it an interesting option to replace Pb in tribological alloys. This work describes the casting process of high-quality thin slabs of Cu-Mg-Sn alloys with different compositions by means of conventional methods. The resulting phases were analyzed using X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray spectroscopy techniques. Typical dendritic α-Cu, eutectic Cu2Mg(Sn) and eutectoid non-equilibrium microstructures were found. Tensile tests and Vickers microhardness show the excellent hardening capability of Mg as compared to other copper alloys in the as-cast condition. For some of the slabs and compositions, cold rolling reductions of over 95 pct have been easily achieved. Other compositions and slabs have failed during the deformation process. Failure analysis after cold rolling reveals that one cause for brittleness is the presence of casting defects such as microshrinkage and inclusions, which can be eliminated. However, for high Mg contents, a high volume fraction of the intermetallic phase provides a contiguous path for crack propagation through the connected interdendritic regions.

Further Discussion on Correlation between Brittleness and Inhomogeneous Network Structure of Cross-Linked Resins Originating in Specific Polymerization Behavior of Triallyl Isocyanurate

Nonfilled triallyl isocyanurate (TAIC) cured resin obtained directly by polymerization of TAIC monomer was too brittle for practical use. The brittleness of cross-linked resins has been thought to be due to the inhomogeneity of their network structures, which consist of colloidal particles as evidenced by electron microscopy. However, the complete loss of flexibility of poly(TAIC) chain does not satisfy the prerequisite of locally enhanced occurrence of intramolecular cross-linking reaction inducing microgelation to form a colloidal particle. Therefore, the correlation between brittleness and network structure of TAIC resins was further discussed, especially focusing on the characterization of resulting TAIC network polymer precursors (NPPs) by size-exclusion chromatography (SEC)−multiangle laser light scattering (MALLS)−viscometry since the ordinary explanation for the brittleness of cross-linked resin does not appear to be the true explanation for TAIC resin’s extreme brittleness. Thus, an alternative explanation for the brittleness of TAIC resins is provided: insufficient growth of the network structure of TAIC resin because of steric hindrance of the cross-linking reaction between sterically crowded growing polymer radical and pendant allyl groups belonging to the rigid primary polymer chain. This imperfection of cross-linking, providing not only insufficient network structure formation but also incorporation of abundant dangling chains into network polymer, could be one of the principal causes of brittleness, even for common cross-linked resins.

Fine structure in the inter-critical heat-affected zone of HQ130 super-high strength steel

The microstructure in the intercritical heat-affected zone (ICHAZ) of HQ130 steel, has been investigated by thermo-simulation test, SEM and TEM. The problem of toughness decrease in the ICHAZ (T p = 800°C) as well as the effect of M-A constituent and carbide precipitation on brittleness was analysed. The test results indicated that the microstructure in the ICHAZ of HQ130 steel was mostly a mixture of lath martensite (ML) and granular bainite (Bg) with a fine but nonuniform grain structure. The cause of brittleness in the ICHAZ was related to production of the M-A constituent in the local region and carbide precipitation. By controlling the welding heat input carbide precipitation and the formation of the M-A constituent can be avoided or decreased.

Low-Temperature Aging Kinetics in Cast Duplex Stainless Steels: Experimental Characterization

Abstract Low-temperature aging (280 to 300°C) of duplex (austenite-ferrite) stainless steels and their resulting long-term loss of toughness is a well-known problem in the energy-producing as well as in other industrial sectors. In order to analyze the problem, the phenomenon was assumed to be thermally activated, accelerated aging at higher temperatures (350 to 400°C) was planned, and the activation energy was estimated. Assuming that the cause of brittleness is the ferrite's spinodal decomposition into the α and α' phases, the present work analyzes the aging kinetics at three temperatures (280, 350, and 400°C) by means of microhardness measurements of the ferritic phase taken in three different duplex stainless steels named after their ferrite content, 12F, 18F and 22F. In view of the microhardness results, an exponential law is proposed to represent the temporal evolution for each of the steels, with three parameters, of which one varies with aging temperature. It should be noted that there is no unique value for the activation energy in all the 280 to 400°C range. This should be divided into smaller subranges for more precision, and here it is shown that in all cases the extrapolation to the service temperature (280°C) of the results obtained in the 350 to 400°C range produces non-conservative results. These results are discussed considering the effect of the G-phase precipitation on the spinodal decomposition kinetics. For assessment applications a mathematical law is proposed that represents the aging kinetics of these steels and that provides reliable results for their service temperature (280°C).

Prevalence and characteristics of brittle diabetes in Britain.

We investigated the prevalence and characteristics of 'brittle diabetes', defined as insulin-dependent diabetes mellitus associated with glycaemic instability of any type, leading to life disruption with recurrent and/or prolonged hospitalizations. A questionnaire was sent to all physicians and paediatricians running diabetic clinics in the UK, from lists held at the British Diabetic Association. A total of 414 brittle patients were reported (72% questionnaire return). Most were young (mean age +/- SD was 26 +/- 15 years), though there was a small peak at ages 60-70 years. There was an excess of females (66%) and overall clinic prevalence was 1.2 per 1000 diabetic patients and 2.9 per 1000 insulin-treated diabetic patients. On average, there was 1.0 brittle patient per diabetic clinic. The most common form of brittleness was recurrent ketoacidosis (59%), with 17% having predominant hypoglycaemia, and 24% mixed instability. Female excess was highest and mean age lowest in the recurrent ketoacidosis group, whilst the reverse was true for those with recurrent hypoglycaemia. Causes of brittleness were offered by 58% of consultants, and most (93%) considered various psychosocial problems as likely underlying factors. We conclude that brittle diabetes is a small but significant problem, currently affecting about 1 per 1000 diabetic patients. Most, but by no means all, are young females--often with recurrent ketoacidosis. Older age groups are more likely to have recurrent hypoglycaemic or mixed types of brittleness. Perceived causes of brittleness are usually psychosocial.

Packing-induced brittleness in polyimide- and aluminum-clad fused-silica capillaries

A variety of fused-silica LC microcolumns have been packed in our laboratory. Some columns became very brittle and essentially impossible to handle without breaking. In some cases, one portion of a packed column would remain flexible while another section would be brittle. In this report the origin and cause of brittleness in polyimide- and aluminum-clad fused-silica packed capillaries is examined.

Brittle Fingernails

Brittle fingernails are characterized by excess longitudinal ridging with distal fracture of the nail plate and by lamellar separation of the distal nail plate. The formation and structure of the nail plate is discussed in order to enable the reader to understand better the pathogenesis and therapy of this disorder. Numerous causes of brittleness are considered, and approaches to its management are suggested. Eliminating the cause of brittle nails offers the best opportunity for cure of this cosmetically disturbing disorder.

タングステンのスェージングエ程における加工性について

Subsequent fabrication of powder metallurgy tungsten rods becomes often difficult because of their brittle fracture in the swaging process. Workable and unworkable lots are sampled to investigate the cause of brittleness in the paractical swaging process of 2.5 mm in diameter. While the fiber structure is well grown to be almost straight in the workable lots, it consists of many discotinuous arrays of wavy fibers in the unworkable ones. There is no direct relation between the workability and the segregation of impurities (O, C) to the boundary of fibers. The deflection to fracture in bending tests reflects the workability well, and the ductility is considerably improved by electropolishing the surface. Tensile tests shows that there is an intrinsic difference in the internal structure between the two lots, which may be caused by different degrees of the development of fiber textures. It is concluded from the results that the practical workability in the swaging process depends on the degree of texture development as well as the roughness of the surface.

Failure processes in particulate filled polypropylene

In this paper the common degradation effect of silicon oxide-filler on fracture strain and fracture toughness of isotactic polypropylene is investigated, analysing the failure processes in the composite material with mmicroscopic methods. Experiments demonstrate that, although fracture of the polymer regions absorbs considerable energy by plastic deformation, void formation and cracking of the interface between polymer and filler usually requires very little energy. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems. The crucial parameters influencing the fracture data of the composite were found to be the cvolume fraction of the filler and the interfacil adhesion between polymer matrix and particles. As the interfacial fracture energy is usally much smaller than ther polymer fracture energy, the composite toughness drops when filler is added. Using a model which describes the individual steps of crack formation and final fracture, an attempt is made to expalin a decrease of crack resistance of teh polymer matrix with increasing filler fraction and to calculate the fracture energy of the composite by introducing partial values of crack resistance of the matrix and the interface, respectively. In Addition, it is discussed how a coarse spherulitic morphology of the matrix, as procduced by isothermal crystallisation dfrom the melt, can modify this behaviour.

Failure processes in particulate filled polypropylene

In this paper the common degradation effect of silicon oxide filler on fracture strain and fracture toughness of isotactic polypropylene is investigated by analysing the failure processes in the composite material by microscopic methods. Experiments demonstrate that, although fracture of the polymer regions absorbs considerable energy by plastic deformation, void formation and cracking of the interface between the polymer and the filler usually requires very little energy. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems. The crucial parameters influencing the fracture data of the composite were found to be the volume fraction of the filler and the interfacial adhesion between polymer matrix and particles. As the interfacial fracture energy is usually much smaller than the polymer fracture energy, the composite toughness drops when filler is added. Using a model which describes the individual steps of crack formation and final fracture, an attempt is made to explain the decrease of crack resistance of the polymer matrix with increasing filler fraction and to calculate the fracture energy of the composite by introducing partial values of crack resistance of the matrix and the interface, respectively. In addition, it is discussed how a coarse spherulitic morphology of the matrix, as produced by isothermal crystallization from the melt, can modify this behaviour.

Fracture of particulate filled polymers

AbstractThe addition of particulate mineral fillers to polymers confers certain mechanical property improvements automatically. Stiffness increases, creep diminishes and distortion at elevated temperatures is often reduced. However, the fracture energy of a polymer, as measured in impact, cracking or tearing tests, may vary quite unpredictably when filler is incorporated. In some special cases the fracture energy increases when small amounts of filler are added although it falls away again at higher volume loadings. This enhancement of polymer toughness by filler is an example of reinforcement. More generally the addition of filler causes a continuous and drastic reduction in fracture energy, resulting in a brittle, weak product.This paper seeks to explain the common degrading effect of filler on polymer fracture energy by considering the progress of a crack through the composite material. The crack travels through regions of polymer and also along the interfaces between polymer and filler. Experiment demonstrates that, although fracture of the polymer regions absorbs considerable energy, fracture of the interfaces usually requires very little. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems.This idea was quantified for thermoplastics such as low density polyethylene and poly (methylmethacrylate) filled with colloidal silica by twin‐roll milling. Where the interfacial adhesive energy was much smaller than the polymer fracture energy, the composite toughness dropped as predicted when filler was added. The particle size, the nature or dispersion of the filler, and the crystallinity of the polymer used, had little influence on this phenomenon, as pointed out theoretically.The crucial parameters influencing the fracture energy of the filled polymer were found to be the volume fraction of filler and the interfacial adhesion between polymer and filler. By chemical treatments the adhesive energy between filler and polymer was raised until the interface was almost as tough as the polymer itself. In this case the filled polymer showed good fracture toughness, lending further support to the theory.

Hydrogen Embrittlement of Electroless Copper Deposits

Transmission and scanning electron microscopes were used to investigate the cause of brittleness of electroless copper deposits. Numerous voids were found in brittle deposits, whereas ductile deposits contained significantly fewer voids. These voids were 20–300Å in diameter and randomly distributed within a grain. Low angle grain boundaries contained larger voids. The ductility was found to improve considerably on prolonged standing even at room temperature. These results, in conjunction with chemical mechanistic considerations, have led to the conclusion that these voids contain hydrogen gas, and that the brittleness is due to the so‐called “hydrogen embrittlement” phenomenon rather than the incorporation of or morphological effects postulated by some investigators.

The mechanical properties of α-phase low-carbon Fe-Mn alloys

An attempt has been made to assess the potential of low-carbon Fe-Mn alloys as a replacement for nickel steels, by measuring the susceptibility of lath martensites in the 4 to 10 pct Mn range to brittle fracture. The alloys were all brittle, but this was not caused by any inherent effect of manganese on the flow properties of iron, such as changes in the σi orKy parameters. The most likely cause of brittleness was found to be a classical temper brittleness effect.

Metallurgy and Magnetic Properties of an Fe-Co-V Alloy

A comprehensive study of the Fe-49% Co-2% V alloy has revealed many new aspects of the metallography of the alloy and led to a better understanding of its mechanical and magnetic properties. Results of the study necessitate revision of previous reports on the metallography by Greiner and Ellis and Köster and Schmidt. In addition to the well-known phase transformation of γ(fcc) to α(bcc) and the ordering of the αphase, a martensitic transformation has been established. The rapid kinetics of theγ→α transformation can be suppressed by drastic quenching in favor of a diffusionless transformation. Martensite is a metastable bcc structure which decomposes slowly into ordered α at intermediate temperatures. Ordering of the α phase is accompanied by pronounced grain refining. X-ray diffraction studies, elevated temperature measurements of saturation, and metallographic examination have not, however, confirmed the decomposition of the ordered α phase suggested by Greiner and Elli. The problem of brittleness has been broadly investigated. Cleavage fracture is a major cause of brittleness. Other causes include the gaseous (hydrogen and oxygen) embrittlement at grain boundaries and the cracking at the incoherent interface between the α phase and martensite. Unless specially treated,all bcc constituents, including disordered α, are inherently susceptible to cleavage fracture. The effect of order on the susceptibility to cleavage fracture and the multiple functions of quenchingin the attainment of ductility have been elucidated in terms of current theories of cleavage fracture and lattice imperfections. The main purpose of quenching is to produce a martensitic structure. Only when a ductile matrix has been prepared, can ordering exert an adverse effect on the ductility of the alloy. Measurements of saturation magnetic moment at elevated temperatures disclose a 2% increase caused by ordering. Room-temperature magnetization curves are compared for different microstructures. The electronic configuration outside the argon core of vanadium atoms is discussed in relation to the composition variation of the average magnetic moment of Fe-Co-V alloys.

Strain–Age Hardening and Brittleness in Chromium

CURRENT theories of the cause of brittleness in ‘pure’ chromium ascribe the phenomenon to Cottrell locking1, invoking the Mott–Stroh2,3 theory of crack formation as the operative mechanism of brittle fracture, and nitrogen as the associated interstitial solute atom. There are several features of the tensile behaviour of annealed chromium (containing approximately 0.002 per cent nitrogen and 0.015 per cent oxygen), however, which this picture does not wholly explain, namely: (1) the very high temperature up to which embrittlement extends (about 350° C.) compared with other body-centred cubic metals of similar structure such as α-iron, molybdenum and tungsten; (2) the abrupt nature of the transition from a highly ductile condition to a completely brittle one, behaviour which again differs markedly from other body-centred cubic metals; (3) the fact that embrittlement occurs (at this nitrogen level) at the bottom of a trough in the maximum stress/temperature and yield stress/temperature curves just below 350° C.4, and not on the steeply rising part of the yield stress/temperature curve, which occurs only below 200° C., and which has been ascribed directly to Cottrell locking.

電氣爐鑄鐵の性質に就て(II)

Owing to investigate the properties of cast iron melted by an electric furnace, we have freshly held the Matsumura's repeated test and O2 analysing test, and report its test results.The results obtained are summarised as follows:(1) Cast iron melted by an electric furnace contains more O2 (FeO) and H2gas than melted by cupola.(2) The more the O2 (FeO) content, the more abnormal the graphite distribution. The more abnormal the graphite distribution, the lower the impact value. This is the cause of brittleness of cast iron melted by an electric furnace.(3) The more the H2content, the more easily be found the sbrinkage cavity. This is the cause of shrinkage cavity of cast iron melted by an electric furnace, we assumed.

鋼の熱脆性に及ぼす熱処理及び成分の影響

There are various kinds of heat-brittleness of steel, these being more or less related to the cracks due to the cooling or forging of steel, the defects of steel at high temperatures, etc. The characteristics and causes of the heat-brittleness are not yet fully revealed. The author, therefore, carried out experiments on the relation of the heat-brittleness and heat-treatment, using two kinds of carbon steel and one kind of nickel-chromium steel. It was thereby concluded, that (1) the precipitation hardning of super-saturated cementite disolved in cr iron at a temperature below the transformation point becomes the cause of brittleness at a lower temperature independent to the blue-shortness, (2) the temperature at which the blue shortness occurs is invariable to the cooling velocity provided that martensite is not formed, and (3) the so called secondary brittleness appears only when the crystal grain is coarsened by annealing at a high temperature such as forging temperature. Next, experiments were carried out on about 30 different special steels. It resulted in the conclusion that (1) all the elements, C, Ni, Cr, Mo, Mn, Si, etc, augment the secondary brittleness, particularly the effects of C and Mn being most remarkable ; (2) Cr and Mn shift the secondary brittleness to a lower termperature; (3) there are a special brittleness near the transformation point which seems to be related to Si and Mn content but even in the steel of the same compositions the special brittleness occurs if the melting differs.