A simple method for evaluating cemented carbides

A simple method is proposed whereby meaningful comparisons can be made between the mechanical properties of cermet cutting tool materials. The method is based upon a test originally described by Palmqvist, but includes a procedure for analyzing the data which makes the test much more useful. Thus, it is shown experimentally and analytically that the parameters measured by the Palmqvist test, the crack resistance parameter,W, (which is shown to be linearly related to the critical strain energy release rateG _IC) and the hardness,H, are related by the following expression 1/W=AH-B whereA andB are constants. The significance of this result is that it can be employed to quickly classify experimental carbide/binder combinations according to their potential as cutting tool materials havingboth high hardness and good resistance to impact. Thus, a few simple measurements to establish the constantsA andB appropriate to the carbide/binder combination under investigation allow a ready comparison to be made with another system for which the constants have previously been established.     

A pilot-plant method for the preparation of complex carbides

Conclusions A study was made of the conditions of preparation of the complex carbides Ta_0.4W_0.6C, V_0.4W_0.6C, Nb_0.4W_0.6C, and Ta_0.4Mo_0.6C on a pilot-plant scale. It was found that the optimum method for the preparation of these complex carbides consists in sintering, for 4 h, charges containing a simple carbide, tungsten (molybdenum), and carbon black in a resistance furnace with a graphite heating element at 2500° C for Ta_0.4W_0.6C, Nb_0.4W_0.6C and Ta_0.4Mo_0.6C and at 2200° C for V_0.4W_0.6C.Translated from Poroshkovaya Metallurgiya, No. 2 (146), pp. 92–95, February, 1975.     

焦炭在高炉中热态性能评价指标初探

对焦炭在高炉中热态性能评价指标进行了研究探索,得出了焦炭反应性、反应后强度、光学组织指数,可以反应焦炭在高炉中热态性质。为焦化厂提供了预测和提高焦炭质量的分析方法。     

Microstructural characterization of self-propagating high-temperature synthesis/ dynamically compacted and hot-pressed titanium carbides

Titanium-Carbide produced by combustion synthesis followed by rapid densification in a high-speed forging machine was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The density of the combustion synthesized/dynamically compacted TiC reached values greater than 96 pct of theoretical density, based on TiC_0.9, while commercially produced hot-pressed TiC typically exceeded 99 pct of theoretical density. The higher density of the hot-pressed TiC was found to be attributable to a large volume fraction of heavy element containing inclusions. The microstructure of both TiCs consists of equiaxed TiC grains with some porosity located both at grain boundaries and within the grain interiors. In both cases, self-propagating high-temperature synthesis (SHS)/dynamically compacted (DC) and hot-pressed, the TiC is ordered cubic (NaCl-structure,B ₁; Space Group Fm3m) with a lattice parameter of ≈0.4310 nm, indicative of a slightly carbon deficient structure; stoichiometric TiC has a lattice parameter of 0.4320 nm. For the most part, the grains were free of dislocations, although some dislocation dipoles were found associated with the voids within the grain interiors. In one SHS/DC specimen, a new, complex Ti-Al-O(C) phase was observed. The structure could not be matched with any previously published phases but is believed to be hexagonal, with a c-axis/a-axis ratio of ≈6.6, similar to the AlCTi₂ phase which has a point group 6 mmm. In all other SHS/DC TiC samples, the grains and grain boundaries were devoid of any second-phase particles. The hot-pressed TiC exhibited a greater degree of porosity than the SHS/densified specimens and a large concentration of second-phase particles at grain boundaries and within grains. The structure and composition of these second-phase particles were determined by con-vergent beam electron diffraction (CBED) and X-ray microanalysis. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

A model for the thermal properties

Thermal properties are important to several applications for powder metallurgy products. For example, liquid-phase sintered tungsten-copper composites are used in microelectronic packaging to obtain a high thermal conductivity in a low thermal expansion material. This article addresses modeling the thermal properties for composites fabricated by liquid-phase sintering. A computational cell is constructed with interlinked phases, consisting of a core of low thermal expansion material (tungsten) and a edge network of high thermal conductivity phase (copper). This structure is used to calculate the composition effects on the coefficients of thermal expansion and thermal conductivity. The results are applied to prior reports on W-Cu and used as a basis to identify several candidate high thermal conductivity systems for future development.     

A proposed method for evaluating short-term exposure condition

High short-term exposure to toxic chemicals can occur during a workday, even if the daily average exposure is lower than the permissible exposure limit, because the exposure concentration varies from minute to minute. To protect workers from acute health effects due to high short-term exposure, the Japan Society for Occupational Health recommends that the maximum value for 15-min time-weighted average (15-min TWA) exposure during a workday should not exceed 1.5 times the occupational exposure limit for 8-hr TWA, and the American Conference of Governmental Industrial Hygienists issues the threshold limit value-short-term exposure limit (TLV-STEL), that is a 15-min TWA exposure which should not be exceeded at any time during a workday. A workday (8 hr) consists of thirty two 15-min periods. If the thirty-two 15-min TWAs are measured, the short-term exposure situation can be appropriately evaluated by comparing the highest measured value with the standard value (e.g. TLV-STEL), but such continuous monitoring consumes a lot of cost and time. In this paper, we propose a method for evaluating short-term exposure by using three or more measured values. This evaluation method corresponds to two different types of selection of sampling periods. One is a random selection of three or more 15-min periods among the 32 periods. If this selection is adopted, a comparison between the 98.44 percentile of the within-day distribution of 15-min TWAs and the standard value can be made by using one-sided tolerance factors, KI, KII and KIII, and the exposure situation is classified into four exposure classes at 95% and 50% confidence levels. Another is a random selection among high exposure periods. If this selection is adopted, a comparison between the specific percentile of the distribution and the standard value can be made with modified one-sided tolerance factors, and the exposure class is determined similarly. This method can provide a precise evaluation of exposure, so that it is useful in the industrial hygiene field.     

钢中微细夹杂物的评价方法

为了对钢中微细夹杂物进行有效的分析评价,本文以氧化物冶金工艺引入的小粒径、均匀且弥散分布的夹杂物为例,建立了一种对微细夹杂物的粒径及分布、成分和形貌进行分析评价的方法。以扫描电子显微镜、透射电子显微镜和能谱分析仪相结合对钢中微细夹杂物进行分析,发现了采用氧化物冶金工艺的钢中夹杂物主要成分所生成的粒子为以MgO、CaO为核心,外层包缚着MnS的细小夹杂物;含Mg的氧化物粒子的形状为长方体, 表面平整光滑,边缘处棱角分明, 大小约为1 μm×0.8 μm×0.3 μm。同时还发现用氧化物冶金工艺的钢其微细夹杂物数量明显高于用常规冶炼工艺的钢。采用本方法可以对钢中微细夹杂物进行较为系统、全面的评价分析。     

A new method for evaluating antiarrhythmic drug efficacy

To develop standards for distinguishing antiarrhythmic drug effect from spontaneous variability of premature ventricular complexes (PVCs), 21 males (mean age 56 +/- 8 years) with chronic ischemic heart disease and PVCs underwent symptom-limited treadmill exercise testing and 24-hour ambulatory monitoring before and after 2 weeks of placebo medication. Linear regression analysis was used to describe the relationship between baseline and placebo PVC frequency for various indexes of ventricular ectopic activity and to establish 95% and 99% one-tailed confidence intervals for this relationship within the group of 21 patients. The lower limit of baseline PVC frequency for which the procedure could distinguish a placebo from a true drug response, termed the "sensitivity threshold," was an average frequency of 2.2 PVCs/hour for ambulatory electrocardiographic monitoring and 1.2 PVCs/min for treadmill exercise testing. All patients exceeded the sensitivity threshold on baseline ambulatory ECGs, but only 38% of patients did so on baseline treadmill exercise tests. To establish antiarrhythmic efficacy with 95% confidence, the minimal percent reduction of PVCs between baseline and placebo visits was 68% for treadmill exercise testing and 65% for ambulatory electrocardiography. Although these standards were developed in patients with chronic ischemic heart disease, the model can be used to establish antiarrhythmic drug efficacy in any patient group.     

A method for predicting sequelae to meningitis.

Reviews medical and behavioral literature for concomitants to meningitis that might predict the likelihood of intellectual sequelae to the disease. Five variables were identified: (a) occurrence and controllability of seizures, (b) time lapse between onset of the illness and treatment, (c) length of hospitalization, (d) patient's age at time of illness, and (e) concentration of bacteria in the cerebrospinal fluid. These variables were used to form a 5-item checklist for rating meningitis patients at the time of dismissal from the hospital. The possibility that such early observations might relate to later development in a manner similar to the Apgar Scale, which is employed at birth, is discussed. It is concluded that physicians and behavioral scientists need to become more aware of intellectual sequelae to meningitis and the variables related to it. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new method for evaluating the rheological properties of the erythrocytes in surgical patients with endogenous intoxication

An examination of 30 patients against the background of using both the operative and conservative methods of treatment was performed in order to study the rheological properties of blood and selection of the most informative tests for diagnosis of microcirculatory disturbances in diseases of the gastrointestinal tract and gastroduodenal area. The authors propose methods of investigation of deformability and viscosity of erythrocytes in patients with the surgical diseases in question. The methods are simple, quite handy for any surgical hospital and polyclinic laboratories. In addition to being used in investigations of the aggregative ability of erythrocytes and viscosity of the whole blood, these methods can be of use in express diagnosis of rheological disorders. The endogenous intoxication in patients with the diseases in question was found to be accompanied by deep rheological disturbances. The deformability of erythrocytes and their viscosity index which can pass ahead of the shifts in other parameters characterizing the hemocoagulative and rheological properties of blood are changed. A conclusion is drawn that the parameters of the erythrocyte deformability and viscosity can be an additional criteria of the adequacy of therapy used for patients with the diseases in question.     

A numerical method for computing hydrometallurgical activity-activity diagrams

A modification of the DIAGRAM computer program has been developed to facilitate graphical representation of hydrometallurgical equilibria. The method is based on dissociation equations with corresponding log equilibrium constants, K_i, and log reaction quotients, Q_i; K_i equals Q_i at equilibrium. The ith dissociation equation is written in terms of Q_i, the log activity of the ith metallic species (P_i), and a certain set of variables (V_j), representing the log activities of species whose stability fields are not to be plotted (e.g., log{Me²⁺}, log{e}, log{H⁺}):

$\text{Q}{}_{\mathrm{i}}\text{= B}{}_{\mathrm{i}}\text{P}{}_{\mathrm{i}}\text{+}\text{∑}\text{j=i}\text{n}\text{C}{}_{\mathrm{ij}}\text{V}{}_{\mathrm{j}}$

where B_i is the reaction coefficient of the ith metallic species in the ith dissociation equation, and C_ij is the reaction coefficient of the jth variable in the ith dissociation equation. One of the variables is designated the balancing variable and allows comparison of the relative stability of any two metallic species to be made in terms of a single equation. By means of the balancing variable, the program generates internally the m(m?1)/2 relative stability equations linking pairs of the m metal-containing species. The stability region of each metallic species is then determined by a systematic scanning of the plotting area using the criterion (K_L>Q_L?). DIAGRAM can calculate and plot stability diagrams using any two of the system variables. Thus not only Eh-pH diagrams, but additional plots of log {Metal}-pH, log{Metal}-Eh, log{NH₂ + NH₄⁺}-pH, etc. can be generated readily. The numerical and thermodynamic bases of the program are described and the capability of DIAGRAM is illustrated with some selected hydrometallurgical examples.     

A standardized method of evaluating exercise-induced asthma

In order to evaluate drug effects on exercise-induced asthma, and to study associated metabolic and pulmonary effects, a method for inducing a consistent response is needed. A method is presented, consisting of 5 min of treadmill exercise sufficiently strenuous to increase a subject's heart rate to 90% of the predicted maximum for age; the airway response is measured frequently for 20 min after exercise. Using this method, 48 asthmatics and 13 nonasthmatics were evaluated. Although none developed severe asthma, a significant airway response occurred in 71% of asthmatics. The severity of exercise-induced asthma depended on intensity and duration of exercise but not on time of day. The method described allows a consistent stress to be applied to a wide age range, and response to this stress was consistent at various ages. Variation of a subject's response following repeated testing was less than that reported with other methods, and could be further reduced by selecting only those subjects with greater than 20% change in one-second forced expiratory volume (FEV1) and by completing studies in less than a month.