Homogenization of Precipitation Hardening Nickel Based Superalloys

Allvac 718 Plus and Haynes 282 are relatively new precipitation hardening nickel based superalloys with good high temperature mechanical properties. In addition, the weldability of these superalloys enhances easy fabrication. The combination of high temperature capabilities and superior weldability is unmatched by other precipitation hardening superalloys and linked to the amount of the γ’ hardening precipitates in the materials. Hence, it is these properties that make Allvac 718 Plus and Haynes 282 desirable in the manufacture of hot sections of aero engine components. Studies show that cast products are less weldable than wrought products. Segregation of elements in the cast results in inhomogeneous composition which consequently diminishes weldability. Segregation during solidification of the cast products results in dendritic microstructure with the segregating elements occupying interdendritic regions. These segregating elements are trapped in secondary phases present alongside γ matrix. Studies show that in Allvac 718Plus, the segregating phase is Laves while in Haynes 282 the segregating phase is not yet fully determined. Thus, the present study investigated the effects of homogenization heat treatments in eliminating segregation in cast Allvac 718 Plus and Haynes 282. Paramount to the study was the effect of different homogenization temperatures and dwell time in the removal of the segregating phases. Experimental methods used to both qualify and quantify the segregating phases included SEM, EDX analysis, manual point count and macro Vickers hardness tests. Main results show that there is a reduction in the segregating phases in both materials as homogenization proceeds hence a disappearance of the dendritic structure. In Allvac 718 Plus, plate like structures is observed to be closely associated with the Laves phase at low temperatures and dwell times. In addition, Nb is found to be segregating in the interdendritic areas. The expected trend of increase in Laves as a result of the dissolution of the plate like structures at the initial stage of homogenization is only detectable for few cases. In Haynes 282, white and grey phases are clearly distinguished and Mo is observed to be segregating in interdendritic areas.

A dislocation based theory for the deformation hardening behavior of DP steels : Impact of martensite content and ferrite grain size

A dislocation model, accurately describing the uniaxial plastic stress-strain behavior of dual phase (DP) steels, is proposed and the impact of martensite content and ferrite grain size in four commercially produced DP steels is analyzed. It is assumed that the plastic deformation process is localized to the ferrite. This is taken into account by introducing a non-homogeneity parameter, f(e), that specifies the volume fraction of ferrite taking active part in the plastic deformation process. It is found that the larger the martensite content the smaller the initial volume fraction of active ferrite which yields a higher initial deformation hardening rate. This explains the high energy absorbing capacity of DP steels with high volume fractions of martensite. Further, the effect of ferrite grain size strengthening in DP steels is important. The flow stress grain size sensitivity for DP steels is observed to be 7 times larger than that for single phase ferrite.

”En aktiemarknad för alla” : Integritet och marknadsomsorg i (själv)regleringen av den svenska värdepappersmarknaden

”A stock market for all”. Integrity and concern for the market in the (self-)regulation of the Swedish securities market This article deals with the transformation process that led to the substantial growth of the securities markets, and also led to a situation where Sweden became one of the leading countries when it comes to ordinary people investing in shares and mutual funds. The article discusses how social control and regulation of the market changed as a result of this process. A sudden and strong unanimity for knowledge tests in order for a stockbroker to be allowed to conduct brokerage, advisory services and asset management was the significant change in this transformation process. Knowledge tests were first introduced on a voluntary basis by the industry itself, but is now a mandatory requirement by the State. This article argues that the unanimity for knowledge tests best can be understood by studying the broadening of the financial markets. The broadening meant that more groups in society – with very varying capabilities – had started to place their assets in the security markets. They were encouraged to do so since this was considered to be the solution to the growing number of socioeconomic problems. This article is mainly based on market statistics and document analysis supplemented by interviews.

Abilities and Cultural Understanding through Literature in the EFL Classroom : - A Literature Review

The English language can be seen as a lingua franca of contemporary times. Its spread and use in the globalized world has affected most levels of society and it can be argued that, in current times, English is synonymous with communication. This need for communication has shaped the English as a Foreign Language (EFL) syllabus, which is evident in the Swedish national steering documents for the educational system. For the upper secondary school these documents show an emphasis on communication, on cultural understanding, and also on the use of literature within the EFL classroom. The need to possess communicative abilities and cultural understanding, in connection with the use of literature, has sparked an interest to investigate if and how literature itself can be used as a tool to develop and improve EFL students’ communicative skills and cultural understanding. This literature review thesis analyzes five international research articles from different geographical parts of the Globe. The findings are categorized, compared, synthesized, and finally discussed in order to answer the research questions asked, and also compared with the English subject syllabus for the Swedish upper secondary school. The findings indicate that the analyzed articles share a consensus, to a varied degree, regarding the positive aspects of literature use in the EFL setting. The arguments are that communicative skills and cultural understanding are intertwined - enabling each other to exist, develop, and improve. One cannot exist fully without the other, and literature is a good tool to use to develop and improve these abilities. Literature can help develop all skills needed to acquire and produce both written and spoken English, and it also enables cultural understanding and a broadening of the mind. Where the articles differ somewhat is in the ideas of why literature is a good tool, how to implement literature in the classrooms, and what some of the negative aspects might be. The thesis also brings the lack of Swedish studies within EFL to the readers’ attention, as well as the need to do more research focusing on the students’ perspectives towards literature use in the EFL setting.