Tailor-made 비정질 합금에서 구조-특성간 상관관계 규명

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 2. 신광선.Since amorphous alloys have disordered atomic structures that are different from those of crystalline alloys, they exhibit various unique properties that can not be explained by conventional theory. In particular, when the amorphous material increases in size, It is very likely to be applied as However, unlike crystalline alloys, amorphous alloys have disadvantage that surplus breakdown occurs at the same time as breakdown because there are no plastic deformation mechanisms such as slip or dislocation. In addition, due to the amorphous forming ability(which requires a rapid cooling rate), it is difficult to fabricate a general metal manufacturing processtherefore, there is a limitation in the size of amorphous material. Therefore, to expand the possibility of using amorphous materials as structural materials, it is essential to improve the plastic deformation resistances of the materials and to enlarge them while maintaining the amorphous structure. Therefore, in this study, we analyzed the atomic- scale structural change of an amorphous alloy depending on the added element and experimentally investigated the change of physical properties according to the structural change. As a result, we overcame the limit of application of existing amorphous materials as a structural material, We propose a concept to control the structure. In addition, we tried to overcome the limitations of existing amorphous alloys by studying enlargement through additive manufacture of amorphous powders using 3D the printing process, which is a leading innovation in manufacturing technology. To investigate the structural and physical properties of a monolithic amorphous phase, a simple binary system (Ni-Nb) was selected and a series of elements (Zr, Gd, Y) was added to the alloy. When Zr (+4 kJ/mol), which has a relatively small positive heat of mixing, was added to the Ni-Nb binary alloy, no heterogeneity could be confirmed in monolithic amorphous phase through transmission electron microscopy or SAXS (small angle X-ray scattering). However, as a result of confirming the interatomic bonding distance and coordination number using EXAFS (extended X-ray absorption fine structure), local atomic-scale heterogeneity in the single amorphous phase was confirmed due to the addition of Zr. In addition, the local atomic-scale heterogeneity could provide several sites where shear bands can be generated, thereby preventing sudden destruction by a concentrated shear band and ultimately improving the amorphous stretching. These results were the first to be experimentally identified. In addition, the correlation between heterogeneity at the atomic scale and the physical properties was confirmed through bulk specimens. It was influenced by the cooling rate. On the other hand, when Y and Gd (+30 kJ/mol), which have positive heats of mixing with constituent elements, were added to the Ni-Nb binary alloy, a phase-separated amorphous phase was obtained. The microstructures and thermal properties of amorphous phase separation were different despite having the same enthalpy of mixing. Based on the thermodynamic data, we developed a new alloy design concept to control the microstructures of phase separated amorphous alloys by calculating the miscibility gap of the phase separated amorphous material (which can induce differences in microstructure) and examining the governing factor. To overcome the size limitation of amorphous material, we observed that the change of physical properties of the printed result varied according to process variable control, which was confirmed through 3D print(powder bed fusion) processing of the amorphous powder. By using the amorphous powder, the amorphous structure could be enlarged while retaining the amorphous structure when the process parameters and the heat input of 3D printing were controlled appropriately. In addition, the amorphous mechanical behavior experiment (produced by 3D printing) showed a difference in cooling rate within a single amorphous state during amorphous manufacture through 3D printing, unlike conventional amorphous manufacturing, It was found that atomic-scale heterogeneity in the single amorphous phase can increase elongation of the amorphous phase. A broad understanding of the amorphous structure and property relationships from this work will ultimately provide a new way to design and process various alloys to take advantage of the excellent properties of amorphous materials. Furthermore, a new milestone for manufacturing customized amorphous materials for their industrial application is suggested.Chapter 1.Introduction 1 1.1.Metallic glasses 1 1.1.1.Definition of metallic glasses 1 1.1.2.Development of metallic glasses 2 1.1.3.Application of metallic glasses 5 1.2.Deformation of metallic glasses 8 1.2.1.Deformation mode of metallic glasses 13 1.2.2.Plastic deformation of metallic glasses 22 1.3.Improvement of plasticity of bulk metallic glasses 25 1.3.1.Ex-situ formed bulk metallic glass composites 26 1.3.2.In-situ formed bulk metallic glass composites 26 1.4.Phase separation in metallic glasses 29 1.4.1.Thermodynamic background phase separation 33 1.4.2.Mechanism of phase separation 38 1.5.Additive manufacturing 42 1.5.1.Type of additive manufacturing 42 1.5.2.Metal additive manufacturing 46 1.5.3.Powder bed fusion additive manufacturing 52 1.6.Research Objectives 56 Chapter 2.Experimental Procedures 58 2.1.Sample preparation 58 2.1.1.Arc melting 58 2.1.2.Melt spinning 58 2.1.3.Injection casting 59 2.1.4.Atomization 59 2.1.5.SPS 62 2.1.6.Laser PBF AM 62 2.2.Microstructural characterization 64 2.2.1.X-ray diffraction 64 2.2.2.Scanning electron microscopy 64 2.2.3.Transmission electron microscopy 64 2.2.4.Small angle X-ray scattering 65 2.2.5.Extended X-ray absorption fine structure 65 2.3.Thermal and mechanical analysis 69 2.3.1.Differential scanning calorimeter 69 2.3.2.Nano-indentation tests 69 2.3.3.In-situ bending tests 70 2.3.4.Compression test 71 Chapter 3.Development of tailor made metallic glasses by controlling composition 73 3.1.Introduction 73 3.2.Effect of Small Positive Heat of Mixing Between Constituent Elements 77 3.2.1.Microstuctural characterization in Ni-Nb-Zr 77 3.2.2.Deformation behavior in Ni-Nb-Zr 91 3.2.3.Enhancement of plasticity by processing control 97 3.2.4.Discussion 100 3.3.Effect of Large Positive Heat of Mixing RelationshipBetween Constituent Elements 101 3.3.1.Microstuctural characterization in Ni-Nb-(Y, Gd) 101 3.3.2.Governing factors for manipulating microstructure in phase separating metallic glasses 107 3.3.3.Discussion 112 3.4.Summary 112 Chapter 4.Development of tailor made metallic glasses by controlling process 114 4.1.Introduction 114 4.2.Printable powder preparation for additive manufacturing 116 4.2.1.Powder preparation 116 4.2.2.Powder property characterization 119 4.2.3.Discussion 125 4.3.Feasibility assessment of laser powder fusion bed additive manufacturing 127 4.3.1.Building strategy 127 4.3.2.Characterization output of PBF AM 129 4.3.3.Mechanical Properties on output of AM 139 4.3.4.Discussion 152 4.4.Summary 156 Chapter 5.Conclusions 158Docto

KEPCO의 사례를 중심으로

학위논문(석사)--서울대학교 대학원 :행정대학원 공기업정책학과,2019. 8. 이수영.In order to sustain the organization in a changing business environment, it is very important to establish and implement an HR strategy that is linked to the organization's management strategy. It is essential to improve the efficiency of organizational culture, organizational structure, system, and strategy beyond the simple operation and management of the organization, and it is essential to prepare a plan for organizational culture change and upbringing strategy for securing and maintaining human resources in the organization. Therefore, it is very important to emphasize the importance of introductory education for new employees who take the first steps into the organization, and to analyze whether the orientation of introductory education is linked with the organization's job performance. The purpose of this study is to investigate the relationship between educational evaluation tools and job performance, that is, the validity and effectiveness of the introductory education evaluation tool, as a result of introductory education for 1,200 people of KEPCO. For this, the achievement evaluation, the teamwork activity, and the personal contribution of the introductory education evaluation were set as the independent variables. The dependent variable of the job performance was set as promotion, promotion period, and reward. In addition, by setting and analyzing the year of employment (education number), job group, and sex as control variables that can affect the research, The results were as follows. In this study, the objective reliability of the research results was increased by conducting the empirical analysis by securing the promotion and reward data of the research subjects after more than 10 years. In order to examine the relationship between 'promotion' and educational achievement, the first variable of job performance, a binomial logistic regression analysis was conducted. As a result, 'Job Knowledge Assessment' and some of the teamwork activities (Cinema KEPCO) were significantly positive (+). In the relationship between the second dependent variable, 'duration of promotion' and educational performance, multiple regression analysis showed that job knowledge evaluation, part of teamwork activities (management simulation) and personal contribution were significantly negative. However, regression analysis did not show any significant relationship with any independent variables in relation to the third dependent variable 'reward'. Human factors that could affect job performance as control variables such as employed year (education group), job group, gender were used, and both gender and job group showed significant relationship in job performance. This shows that human factors are closely related to job performance. In conclusion, the predictive validity of job performance evaluation, which is an evaluation method similar to the test promotion system of KEPCO, has been relatively high among the tools for evaluating the introductory training of new employees, and suggests that teamwork activities and personal contribution activities are also important for job performance. In the future, it is possible that through objective measurement of various human resource management activities, if we trace and observe the entire process of the research target from the time of starting the organization to the established middle-level employee in the organization, The statistical analysis was carried out using the STATA14 version, using binary logistic regression analysis and multiple regression analysis with empirical data.변화하는 경영환경 속에서 조직의 지속가능성을 위해, 조직의 경영전략과 연계된 HR전략을 수립하고 실행하는 일은 상당히 중요한 일이다. 단순한 조직의 인력 운용 및 관리를 뛰어넘어 조직문화, 조직구조, 시스템, 전략의 효율성을 높이는 역할이 강조되며 조직 내 인재의 확보 및 유지를 위한 조직문화 변화 및 육성전략에 대한 방안을 마련하는 것이 필수적이다. 따라서 조직에 첫발을 내딛는 신입사원들에 대한 입문교육의 중요성이 강조될 수밖에 없으며, 입문교육의 방향성이 조직의 직무성과와 연계되고 있는지를 분석하는 것인 매우 큰 의미를 갖게 된다. 본 연구에서는 국내 대표 공기업인 KEPCO의 2004～2005년 대졸 공채입사자 1,200명을 대상으로 하여, 입문교육을 실시한 결과로서 교육평가도구와 직무성과와의 관계, 즉 입문교육평가 도구의 타당성과 효과성을 분석하였다. 이를 위해, 독립변수로는 입문교육 평가의 성취도 평가와 팀워크 활동 그리고 개인공헌도를 설정하였으며, 직무성과인 종속변수로는 승진, 승진소요기간, 포상으로 설정하였다. 또한 연구에 영향을 미칠 수 있는 통제변수로는 입사년도(교육기수), 직군, 성별 등을 설정하여 분석함으로써 신입사원 입문교육평가 성적이 장기적 직무성과인 승진과 승진소요기간 및 포상에 어떠한 유의한 결과가 있는지를 고찰하고자 하였다. 본 연구에서는 2년간의 입문교육 성적 데이터 및 교육종료 직후가 아닌, 10년 이상의 시간이 흐른 이후 연구대상의 승진과 포상 데이터를 확보하여 실증적인 분석을 시행함으로써 연구결과의 객관적 신뢰도를 높였다고 할 수 있다. 우선, 직무성과의 첫 번째 변수인 승진과 교육성적과의 관계를 살펴보기 위하여 이항로지스틱 회귀분석을 시행하였으며, 그 결과 독립변수 중 성취도 평가인 직무지식평가와 팀워크 활동 중 일부(시네마한전)가 유의한 정(+)의 관계가 있는 것으로 나타났다. 두 번째 종속변수인 승진소요기간과 교육성적과의 관계에서는, 다중회귀분석결과를 통해 독립변수 중 직무지식평가와 팀워크 활동 일부(경영시뮬레이션) 그리고 개인공헌도가 유의한 부(-)의 관계가 있는 것으로 나타났다. 그러나, 마지막 세 번째 종속변수인 포상과 관련하여서는 회귀분석결과, 어떠한 독립변수와도 유의한 관계를 보이지 않았다. 직무성과에 영향을 미칠 수 있는 인적요인을 통제변수로 설정하였는데, 입사년도(교육기수), 직군, 성별, 나이를 사용하였으며, 성별과 직군에 대해서는 직무성과 모두 유의한 관계가 있는 것으로 나타났다. 이를 통해 인적요인이 직무성과와 밀접한 관련이 있음을 확인할 수 있었다. 결론적으로는 신입사원 입문교육평가 도구 中, KEPCO의 시험승진제도와 유사한 평가방식인 성취도 평가의 직무성과 예측타당도가 비교적 높게 나왔으며, 팀워크 활동과 개인 공헌활동도 직무성과에 중요한 의미를 차지하고 있다는 시사점을 보여준다. 향후 다양한 인적자원관리활동의 객관적 측정을 통해, 연구대상이 조직입문시기부터 조직 내의 정착한 중견직원으로 성장해 가는 전 과정을 추적·관찰해 나간다면, 보다 조직에 적합한 인재로 길러낼 수 있는 중요한 자료가 될 수 있을 것으로 판단된다. 분석은 STATA14 버전을 활용하여 실증데이터를 가지고 이항로지스틱 회귀분석 및 다중회귀분석 등을 실시하였다.제1장 서 론 1 제1절 연구의 목적과 필요성 1 제2절 연구대상 및 범위 4 제2장 이론적 논의와 선행연구 검토 6 제1절 신입사원 입문교육에 대한 이론적 논의 6 1. 신입사원 입문교육의 개념과 의의 6 2. 신입사원 입문교육의 목적 11 3. 신입사원 입문교육의 효과성 12 4. 신입사원 입문교육의 구성요소 15 5. 국내 대기업의 신입사원 입문교육 현황 17 제2절 직무성과에 대한 이론적 논의 20 1. 직무성과의 개념과 의의 20 2. 직무성과에 대한 이론적 논의와 관점 21 제3절 신입사원 입문교육과 직무성과와의 관계 26 1. 신입사원 입문교육과 승진 32 2. 신입사원 입문교육과 승진소요기간 34 3. 신입사원 입문교육과 포상 36 제4절 연구의 차별성 37 제3장 연구설계 및 분석방법 …………………38 제1절 분석의 틀 38 제2절 변수의 조작적 정의와 측정방법 39 1. 독립변수 39 2. 종속변수 40 3. 통제변수 40 제3절 분석방법 42 제4장 분석결과 44 제1절 기술적 통계분석과 다중공선성 진단 44 1. 주요변수의 기술통계량 44 2. 상관관계 분석 및 다중공선성 진단 45 제2절 회귀분석 결과 47 1. 승진 모형(가설1 분석) 47 2. 승진소요기간 모형(가설2 분석) 50 3. 포상 모형(가설3 분석) 52 제3절 분석결과 해석 55 1. 입문교육성적과 승진의 관계 55 2. 입문교육성적과 승진소요기간의 관계 57 3. 입문교육성적과 포상의 관계 59 4. 심층 인터뷰 시행 및 결과 60 제5장 결 론 62 제1절 연구결과의 요약과 시사점 62 제2절 연구의 의의와 한계 64 1. 연구의 의의 64 2. 연구의 한계 66 참고문헌 67 Abstract 70Maste