Tsugio Ogura

Application of the selected area channeling pattern method to the study of intergranular fracture in Ni3Al

Abstract The selected area channeling pattern method was applied to the characterization of grain boundaries on the basis of the coincidence lattice site model and to the detection of plastic strain accompanying intergranular fracture in cast or recrystallized Ll 2 type Ni 3 Al and Ni 3 (Al, Ti) polycrystals. The sum of the numbers of low angle and twin (Σ3) boundaries observed was less than 20% of the number of all boundaries studied. An evident resistivity of low angle and Σ3 boundaries against intergranular cracking was found. The boundaries of grains having the coincidence orientation relation (Σ5-Σ29) and random boundaries were preferentially broken under tensile stress. The amount of plastic strain accompanying intergranular fracture of Ni 3 Al was found to depend upon processing conditions (as-cast or as-recrystallized state), deformation temperature, and substitution of titanium for aluminum. It is pointed out that the amount of plastic strain is consistently larger in materials having higher resistivity against intergranular cracking.

Grain boundary fracture of L12 type intermetallic compound Ni3Ai

AES analysis of intergranular fracture surfaces of Ni3Al showed that grain boundaries are free from any detectable amount of impurity segregation. From this finding it was suggested that grain boundary brittleness in Ni3Al is not due to the segregation of harmful elements. X-ray diffraction and SEM observation of the fracture surfaces detected a plastically strained layer of which thickness is compa-rable to grain size.

Microstructures of deformation and fracture of cementite in pearlitic carbon steels strained at various temperatures

In order to make clear the effect of temperature on deformation and fracture of cementite in steels, observations by transmission electron microscopy were made on cementite in carbon steels strained in tension at various temperatures ranging from -196 to 700°C. Hardly any plastic deformation of cementite was detected at-196 and-78°C. It was confirmed that above room temperature cementite in steel can deform due to dislocation slip and that the deformation becomes easier as the temperature increases. Slip in cementite at room temperature and at 300°C seems to be confined to only (100) or (001). Dislocations observed at room temperature and at 300°C were mostly isolated and straight. Above 400°C (100), (010), (001), and some {110} planes are all operative slip planes. Dislocation loops, dipoles, cusps, and networks were frequently found. These observations indicate that double slipping and the interaction of dislocations can occur and that the deformability of cementite above 400°C is very large. An appreciable degree of dynamic recovery was detected above 500°C. The fracture of cementite at -196 and-78°C occurred in a cleavage manner along some crystallographic planes such as (110), (100) or (210). Above room temperature fracture occurred along an activated slip plane and was preceded by some amount of slip on that plane. Above 400°C cementite fracture, caused by joining of voids, formed along an activated slip plane was frequently observed.

Dependence of phosphorus segregation on grain boundary crystallography in an FeNiCr alloy

Abstract Relation between the amount of P-segregation and grain boundary crystallography in an FeNiCr alloy was studied. A grain boundary etching method was utilized for analyzing P-segregation, and the crystallography of grain boundaries was characterized by making channelling pattern and trace analysis. Macroscopic geometric characteristics of grain boundaries which were found to be effective in suppressing the amount of P-segregation are (1) low-angle disorientation (2) σ3 orientation relation, (3) \ gs3 (quasi-twin) orientation relation (4) boundary orientation close to the orientation of the coherent twin boundary,(5) boundary plane having low indices, and (6) boundary straightness. It was suggested that an essential geometric factor on the atomic scale which controls the amount of P-segregation in high-angle boundaries is their coherency or free volume.

A grain boundary etching method for the analysis of intergranular P-segregation in iron-based alloys

The effectiveness of a grain boundary etching method for the non-destructive analysis of intergranular segregation of P in iron-based alloys was examined by using a saturated aqueous solution of picric acid containing sodium tridecylbenzene sulfonate. Among all the alloys examined only those doped with P suffered selective etching attack against grain boundaries. The degree of the etching attack in a P-doped NiCr steel was found to have a linear relation with the concentration of grain boundary P as measured by Auger electron spectroscopy. From these evidences, the grain boundary etching method was concluded to be useful as a technique analyzing the grain boundary concentration of P in NiCr steels. The application of the method was successfully made to CrMo and C-free NiCr steels which are hard to exhibit perfect intergranular fracture. The application was not successful to Fe-40 pct Ni and Fe-3 pct Si alloys whose surfaces were unstable electrochemically compared with those of NiCr and CrMo steels.

Dynamic compaction of amorphous Ni75Si8B17 and Pd78Cu6Si16 alloys

Amorphous Ni75Si8B17 and Pd78Cu6Si16 alloy powders were dynamically compacted using a propellant gun. The degree of compaction increases with increase in the magnitude of shock pressure. The shock pressure giving the highest degree of compaction is lower in Pd78Cu6Si16 than in Ni75Si8B17. The progress of compaction-induced crystallization is faster in Pd78Cu6Si16 than in Ni75Si8B17, reflecting the difference in their exothermic characteristics during heating. Evidence was found for a melting and solidification mechanism of dynamic compaction of amorphous powders.

Temper Embrittlement Diagram of NiCr Steel Doped with Phosphorus

The temper embrittlement equation of a P-doped NiCr steel and the McLean’s equation for equilibrium intergranular segregation of P in the same steel were derived experimentally. On the basis of these equations, two-dimensional temper embrittlement diagrams were constructed. It was shown that the construction of a temper embrittlement diagram offers a way to predict the ultimate level of temper brittleness of steels.