Residual Stress Anisotropy Research Articles

Residual stress anisotropy, stress control, and resistivity in post cathode magnetron sputter deposited molybdenum films

As part of the program to develop a large-area thin-film pulse heater for a lithium ion source, the residual stress in post cathode magnetron sputter deposited molybdenum films has been studied. It was found that in films prepared in the low-pressure sputtering regime, the residual film stress is very sensitive to the gas pressure during sputtering and that the film stresses are highly anisotropic. The transition pressure for changing from compressive to tensile residual stress, as defined by Thornton and Hoffman, depends on the relationship between the measurement direction in the film and the post cathode orientation. In order to deposit a nearly stress-free film a pressure cycling technique was developed which deposited alternate film layers containing tensile and compressive stresses. Film resistivity and thermal coefficient of resistivity measurements were made during the pulse heating of the molybdenum films.

Residual Stress, Fracture, and Adhesion in Sputter-Deposited Molybdenum Films

AbstractAtomistically deposited films may form with high residual stresses which may be either tensile or compressive in nature. These film stresses represent stored strain energy which may affect the adhesion of the film-substrate couple and in the limit may cause spontaneous fracture at or near the film-substrate interface (loss of adhesion). In the post cathode magnetron sputter deposition of molybdenum films, we have found that the intrinsic film stresses are generally anisotropic and may easily exceed the fracture or adhesive strength of the film-substrate couple. The residual stress anisotropy in the film is dependent on the orientation with respect to the post cathode and the magnitude and nature of the stresses are very dependent on the deposition conditions, particularly gas pressure during sputtering. By using a pressure-cycling technique, we have deposited thick (5 microns) films of molybdenum which have little residual stress or stress anisotropy.

Magnetic Properties of a Non-Stoichiometric Zn-Mn-Fe Spinel

Magnetic properties of single crystals of the non-stoichiometric spinel Zn 0.36 Mn 0.57 Fe 2.07 O 4 have been studied by 57 Fe Mossbauer spectroscopy. The divalent Fe ions are located only at octahedral sites. The cation distribution was deduced from a spectrum taken with a large magnetic field applied to the sample. A value of the lattice constant was calculated from the distribution and is consistent with a value measured by X-ray diffraction. The magnetic moments of Fe ions are shown to be collinear. Mossbauer spectra confirm that below about 240 K the easy magnetic axis is along the [111] direction. A significant influence of residual stress anisotropy on the intensities of Zeeman lines is observed at temperatures close to 240 K.

X-Ray Measurement of Residual Stress Induced in Steel Sheets Deformed by Tension in Two Alternately Orthogonal Directions

One of the important problems respecting the X-ray method of stress measurement is concerned with the residual stress induced in polycrystalline metals by plastic deformation. As reported in a previous paper, the axial residual stress induced in an iron specimen by uniaxial tension does not satisfy the so-called macroscopic equilibrium over the cross section of the specimen if measured with respect to {310} lattice planes by Co-Kα radiation. This phenomenon can be sufficiently interpreted by taking into consideration the elastic and plastic anisotropy of each crystal constituting a polycrystalline aggregate, and the selective nature of the X-ray method.In the present study, a thin temper-rolled steel sheet was deformed by stretches given in two alternately orthogonal directions, and the distribution of residual stress induced in the specimen was determined with respect to {310} crystal Planes by application of Co-Kα radiation. The material used in the experiment was also examined in the tension test to see how the flow stress would depend on its direction.The experimental results obtained are summarized as follows:(1) The anisotropy of residual stress is usually observed on the specimen stretched in two altelrnately orthogonal directions as well as on the specimen stretched only in one direction.(2) The compressive residual stress induced in the direction making angles of 0°and 22.5° with the direction in which the preliminary stretch was given, decreases parabolically. It is due to the strain caused by the vertical stretch subsequently given.(3) On the contrary, the compressive residual stress, induced in the direction making angles of 45°, 67.5°and 90°with the direction in which the preliminary stretch was given, increases parabolically together with the strain caused by the vertical stretch subsequently given. However, the rate of increase in the residual stress is much less than that induced by stretching only in one direction.(4) On the specimen that has been deformed by stretch in two alternately orthogonal directions, there is maximum flow stress in the drirection in which smaller preliminary strain was given.

On the Elastic Anisotropy of Residual Stress Induced by the Plastic Deformation of Polycrystalline Metals

The peak shift and line broadening on 0.06%C steel deformed by tension were measured by means of X-ray diffractometer. These values depended on their diffraction plane.In this paper, the change in peak shift and line broadening on the diffraction line was discussed with reference to its elastic anisotropy.The results are as follows.(1) The change in peak shift on the diffraction line was accounted for by considering that the mean residual stress in the grains in which X-ray diffraction occurred was constant.(2) Also the change in line broadening was accounted for by considering that the distribution of micro-stresses in each grain or between the grains in which X-ray diffraction occurred was almost the same.(3) It seems that it was either because the principal stresses in each grain were γ1≈γ2, or because the specimen in this work had texture, that there was but little line broadening due to the difference in the direction of action of the principal stresses.(4) The mean residual stresses measured from peak shift agreed with that which was obtained by the sin2φ method.