钛合金表面激光熔覆氧化锆陶瓷涂层的显微组织     

李平  邓永瑞 《洛阳工业高等专科学校学报》1995,(3)

本文采用激光熔覆技术,探讨制备ZrO_2/Ti梯度功能材料,利用SEM和EPMA分析激光熔覆层,过渡层、热影响区的组织形貌和各组元的成份分布。用X射线衍射和微区X射线衍射技术分析激光熔覆区的氧化锆相变及各区域的相组成。得到:经过激光熔覆处理,熔覆区氧化锆由C—ZrO_2和T—ZrO_2组成,激光熔覆层、过渡区,热影响区的组织分别为ZrO_2枝晶 Ti_2O、粒状Z_rO_2 α相、片状α组成,在过渡区内成份是渐变的,组织为陶瓷相ZrO_2和塑性相α相混合。此工艺是制备ZrO_2/Ti梯度功能材料有前途的方法。  相似文献   

高强度变形铝合金——Al-Zn—Mg-Cu系合金   总被引：1，自引：0，他引：1  

郑虹 《鞍山师范学院学报》2001,3(3):71-73

阐述了不同合金元素对高强度变形铝合金性能的影响，以及提高高强度变形铝合金性能的方法。  相似文献   

型内中心和合金棒温度检测系统的研制     

杨永华  曾辉 《实验室研究与探索》2012,31(1):18-20,96

介绍了以ADuC845单片机为中心控制单元,采用2支铂铑10-铂热电偶,放置在铸型中部和安插在合金棒内,用铜热电阻组成冷端补偿电桥和线性插值查表算法提高了温度测量精确度,研制成一种温度检测系统。该检测系统可以检测高达1 600℃的温度,并通过液晶显示出温度变化的动态曲线图。实验结果表明,系统可以精确测量出钢液温度的变化曲线,从而也表明了铸件的凝固时间。  相似文献   

钛合金表面激光熔覆TiC涂层显微结构和耐磨性     

王慧萍  李军  李芳  李曼萍  奚文龙 《实验室研究与探索》2012,31(2):8-11

采用HL-5000型横流CO2激光加工机在TC4钛合金表面激光熔覆TiC+Ti和TiC+Ti+F102复合涂层。通过SEM、EDAX、XRD、HXD-1000TMC型显微硬度计,HT-600型高温摩擦磨损试验机,分析了熔覆层的显微组织、成分、物相,测试了激光熔覆层的显微硬度和滑动摩擦磨损性能。结果表明,激光熔覆制备的TiC复合涂层与基体呈冶金结合,在TiC+Ti激光熔覆层中,熔覆层的组织是在Ti基体上分布着TiC树枝晶;在TiC+Ti+F102激光熔覆层中,TiC颗粒发生了部分溶解,熔覆层的组织是在Ti基和γ-Ni基的基体上分布着细小的TiC颗粒和TiC树枝晶。TiC+Ti激光熔覆层的硬度约为700 HV0.1,TiC+Ti+F102激光熔覆层的硬度约为800 HV0.1,两种复合涂层耐磨性均比TC4钛合金显著提高。  相似文献   

Who benefits from student aid? The economic incidence of tax-based federal student aid     

Nicholas Turner 《Economics of Education Review》2012

Federal benefit programs, including federal student aid, are designed to aid targeted populations. Behavioral responses to these programs may alter the incidence of their benefits, a possibility that receives less attention in the literature compared to tax incidence. I demonstrate the importance of benefit incidence analysis by showing that the intended cost reductions of tax-based federal student aid are substantially offset by institutional price increases for a sample of 4-year colleges and universities. Contrary to the goal of policymakers, I find that tax-based aid crowds out institutional aid roughly dollar-for-dollar. Unfortunately, it is not clear how institutions utilize these captured resources, so that the ultimate incidence of the programs is uncertain.  相似文献   

Measuring the earnings returns to lifelong learning in the UK     

Jo Blanden  Franz Buscha  Patrick Sturgis  Peter Urwin 《Economics of Education Review》2012

This paper examines the earnings returns to learning that takes place following the conventional ‘school-to-work’ stage of the life-course. We operationalise such ‘lifelong learning’ as the attainment of certified qualifications in adulthood, following the completion of the first period of continuous full-time education. Using data from the British Household Panel Survey (BHPS) for the period 1991–2006, our approach and findings represent an important addition to the existing evidence base. By using annual data, we are able to employ the fixed effects estimator, which eliminates the problem of time-invariant unobserved heterogeneity. Our dynamic specification uses a lag structure to consider how earnings returns evolve in the medium and longer run, whilst also controlling for wage trends which were evident prior to qualification attainment. Our results show a medium-run return for women of 10% on hourly wages. For men, initial suggestions of a similar positive return are eliminated once pre-qualification trends are taken into account. This suggests that adult learning has a causal effect on women's subsequent earnings but, for men, any apparent gain is due to selection.  相似文献   

The redistributive equity of affirmative action: Exploring the role of race,socioeconomic status,and gender in college admissions     

Andrew M. Francis  Maria Tannuri-Pianto 《Economics of Education Review》2012

This paper contributes to research on affirmative action by examining issues of equity in the context of racial quotas in Brazil. We study the experience of the University of Brasilia, which established racial quotas in 2004 reserving 20% of available admissions slots for students who self-identified as black. Based on university admissions data and a student survey conducted by the authors, we find evidence that race, socioeconomic status, and gender were considerable barriers to college attendance and achievement. For example, first-difference regressions involving pairs of siblings indicate that black identity and gender had a negative effect on entrance exam scores. Moreover, we compare displaced and displacing applicants and find that racial quotas helped promote equity to some extent. Nevertheless, the scale and scope of redistribution were highly limited, and the vast majority of Brazilians had little chance of attending college, suggesting that more still needs to be done.  相似文献   

Funding higher education and wage uncertainty: Income contingent loan versus mortgage loan     

Giuseppe Migali 《Economics of Education Review》2012

We propose a simple theoretical model which shows how the combined effect of wage uncertainty and risk aversion can modify the individual willingness to pay for a HE system financed by an ICL or a ML. We calibrate our model using real data from the 1970 British Cohort Survey together with the features of the English HE financing system. We allow for individual heterogeneity by considering different family backgrounds and occupations. We find that graduates from poor families, males and graduates working in the private sector are more willing to pay to switch to an ICL. Using the UK Labour Force Survey we evaluate the distributive effects of our model. We compute the repayment burdens and taxpayer subsidies for average, low and high earnings graduates. The results confirm the important insurance benefits of an ICL compared to a ML, with lower burdens and higher subsidies for poorer graduates.  相似文献   

Do tuition fees affect enrollment behavior? Evidence from a ‘natural experiment’ in Germany     

Malte Hübner 《Economics of Education Review》2012

This paper uses the introduction of tuition fees in seven of the sixteen German states in 2007 as a natural experiment to identify the effects of tuition prices on enrollment probabilities. Based on information on enrollment decisions of the entire population of high-school graduates between 2002 and 2008, I find a negative effect of tuition fees on enrollment behavior. The effect is larger than in existing studies for European countries, but of a similar magnitude as effects identified with U.S. data. A potential spill-over effect of the policy intervention to the comparison group is accounted for by using the estimation results to calibrate a structural model of the enrollment decision.  相似文献   

Math skills and labor-market outcomes: Evidence from a resume-based field experiment     

Cory Koedel  Eric Tyhurst 《Economics of Education Review》2012

We examine the link between math skills and labor-market outcomes using a resume-based field experiment. Specifically, we send fictitious resumes in response to online job postings, randomly assigning some resumes to indicate stronger math skills, and measure employer responses. The resumes that are randomly assigned to indicate stronger math skills receive more interest from employers than the comparison resumes. Our findings add to the body of evidence showing that stronger math skills positively affect labor-market outcomes.  相似文献