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The worldwide spread of COVID-19 first reported from Wuhan in China is attributed to migration and mobility of people In this article, we present how our understanding of migration and livelihood could be helpful in designing a mitigating strategy of economic and social impact of COVID-19 in India We conclude that there are many challenges migrants face during the spread of COVID-19 resulting from nationwide lockdown Many internal migrants faced problems such as lack of food, basic amenities, lack of health care, economic stress, lack of transportation facilities to return to their native places and lack of psychological support On the other hand, COVID-19 has also brought into sharp focus the emigrants from India and the major migration corridors India shares with the world as well There is a huge uncertainty about how long this crisis will last This article further provides some immediate measures and long term strategies to be adopted by the government such as improving public distribution system, strengthening public health system, integration of migrants with development, decentralisation as a strategy to provide health services, and providing support to return migrants to reintegrate them, and also strengthen the database on migration and migrant households © 2020 MIGRATION LETTERS Transnational Press London

India is a country with one of the largest emigrants with 17 million Indians living outside the country compared with 450 million internal migrants. During the 1970s and the 1980s, there was concer...

Rising urbanization and economic inequality are concomitant in India and varies by type of urban localities such as Municipal Corporations, Municipal Councils and Census Towns. Studies on developmental disparities by type of urban localities are limited. Using data from 7229 wards of Maharashtra consisting of 2076 wards from Municipal Corporations, 4738 wards from Municipal Councils, and 278 wards from Census Towns, this study examined the variations in the level of development in the wards of urban Maharashtra. Principal component analysis was used to compute the development index using 19 selected variables. Descriptive statistics and multilevel analysis were used in the analyses. In the composite index of development, Cantonment Boards ranked first, followed by Municipal Corporations and Nagar Panchayats. The variations in the level of development were the highest among Municipal Councils (Mean − 0.69; SD = 2.92), followed by Nagar Panchayats (Mean 0.47; SD = 2.88), and Census Towns (Mean 0.05; SD = 2.34). Around 64% of the variability in the development was explained at the ward level in the multilevel analysis. The study found large variations in development within and between urban localities. It suggests multi-sectoral approach including allocating resources in urban localities based on the level of development and relative population size. Ward development needs to be prioritized to reduce the growing urban inequalities among all three urban localities.

The emigration and internal migration assume significance for Muslims because of their lower socio-economic status and a higher level of deprivations. Muslims constitute 28% of total emigrants compared to 14% in India's total population. Telangana's emigration rate is double that of India. The higher level of unemployment among Muslims could be one of the push factors for emigration. This chapter also investigates the impact of emigration on the health status and health seeking behaviour among Muslims in Telangana. It is found that emigration plays an important role in the progress of households and communities and improves the quality of life. It has a crucial role for the marginal and minority communities who face serious barriers and discrimination not only accessing labour market but also health care.

Purpose The purpose of this paper is to analyze the overall morbidity prevalence and their differentials among emigrants’ and non-emigrants’ wives in Kerala, India. Design/methodology/approach The study is based on the third round of The Kerala Migration Survey-2007 data. The third round of KMS was perhaps the first survey which has collected data on Indian emigration and morbidity scenario during 2007 at the household and individual level. Descriptive statistics, binary logistic regression models, and Oaxaca decomposition models were used to examine the disease differentials among emigrants’ and non-emigrants’ wives. Findings The paper shows that household size is negatively associated with chronic disease and incidence of morbidity is much lower among emigrants’ wives. The result also shows that among women, those who stay with a husband or whose husbands are elsewhere in India show a higher incidence of morbidity than those whose husbands are abroad, owing to the limited scope of activity as well as freedom in lifestyle and for taking independent decisions. Thus, it can be concluded that for women, the scope of activity and the freedom to live are important factors contributing to the level of morbidity. Blinder-Oaxaca decomposition results show that non-poor households and non-Muslim religion are in a disadvantageous position in terms of chronic morbidity. Research limitations/implications This paper is based on the cross-sectional nature of data; this is an obvious limitation on the effect of emigration on morbidity differentials among emigrants’ and non-emigrants’ wives. Originality/value There are few or rare studies conducted so far to investigate the effect of migration on the health of the spouses or families left behind.

This study attempts to understand the process of convergence or divergence of the living conditions across the urban space of Kolkata Municipal Corporation. Evidences are drawn from the ward-level data of Census 2011 and also relevant municipal documents for these four cities.

With a population of 1.21 billion according to the 2011 census, India is a culturally diverse, lower-middle income country located in south Asia. Data on internal migration have been collected since 1971, primarily by means of decennial censuses, with questions focussing on lifetime migration, duration of residence, reasons for moving and mover characteristics, coupled with regular household surveys. Data from the 2011 Census show that Indians exhibit a low level of permanent internal migration with an ACMI below 8%, which is thought to be substituted by temporary circular migration, particularly among males. Indians display early migration profiles, with peaks at age 20 for females and 25 for males, driven largely by marriage for the former and employment for the latter. With about 30% of its population residing in urban areas, India appears to be at an early stage in the urban transition and contribution of rural-to-urban migration to urban growth is not dominant. Moderate levels of migration effectiveness coupled with low intensities underpin limited population redistribution. Spatial patterns reflect pronounced and persistent state-level variations in socioeconomic conditions where developed and urbanised states register net gains while states at lower levels of development record net losses. Despite a low level of permanent internal migration by Asian and global standards, the Indian government remains concerned about rural-to-urban migration around issues of overcrowding and infrastructure provision.

By using unit level data on migration from nationally representative National Sample Survey Organisation (NSSO) for two points of time (1993 and 2007-08), this paper looks at the change in the level of employment related inter-state out migration in India. This paper brings out: the change occurred in the rate of inter-state out-migration between 1993 and 2007-08, the proportion of economically engaged women within the category of women who migrated due to marriage out of their state, the volume of employment related inter-state out migration of women, and finally, the propensity of Indian people for employment related inter-state out migration by their social, economic and geographical attributes. This paper finds a two times increase in inter-state out-migration in India during last one and a half decades. The increase is found even higher in many states/union territories and when we confine the analysis only to the working-age population. The gender gap has been glaring. Compared to 35 males per 1000 working age male population out-migrating across the border of their state of domicile for employment there is only 10 per 1000 working age females. Further female migration in India is predominantly occurs within the state. Out of the total women inter-state out-migrants, 4 percent reported to have migrated exclusively for employment, while more than 80 per cent reported marriage as a reason of migration. In India, economic activity of women is under reported. Keeping this in view, we have tried to adjust the reason of migration for women. This study shows that the adjusted employment related reason of migration for inter-state women rises to 18 per cent at the all India level. The logistic regression analysis further shows that these women who reported marriage a reason of migration but actually part of the workforce belong to lower socio-economic households.

India is known for sending a large number of indentured labour to Africa and Caribbean to work in sugar cane and plantation agriculture during the colonial rule. However, the emigration to the West started after the Second World War, more specifically after 1965, as a result of the liberalisation of immigration policy of US and other western countries. Also, emigration to the Middle East increased rapidly since late1970s as a result of oil boom. Of late, there has been an increase in unskilled and semi-skilled labour emigration from many states of India. Historically Gujarat has been one of the leading states in emigration from of India. It is believed that Gujaratis migrated abroad to work as traders, businessmen, shopkeepers, hoteliers, professionals etc. A comprehensive study of Gujarati emigration which includes the characteristics of emigrants, the individual and household strategies, the process of migration comprising of formal (recruitment agency) and informal channels (family, kin, friends, relig...

Background Mining industries have enormous potential to improve food shortage by providing employment opportunities in its mining vicinity. But, simultaneously, these areas also suffer from ‘resource curse’ due to detrimental effects of mining. Hence, this study examined the effects of coal mining on household food availability and food access among proximate population residing in resource-rich but economically backward mining region of Dhanbad district, Jharkhand, India. The primary data was collected from two compare groups, viz. households from exposed versus non-exposed villages of mining effect under the cross-sectional research design using structured questionnaire between September, 2014, and February, 2015. Both bivariate and multivariate statistics were used to assess the study objectives. Results Finding shows that households from non-mines affected villages were at 40% higher risk of food shortage than household from mines affected villages. Furthermore, odds ratio shows that rise in percentage of expenditure on food also increases the food shortage vulnerability. Female-headed households, below poverty line households and MNREGA card holders households were significantly positively related to food shortage. In contrast, households with membership of any socio-political organization and more than 2 acres of farmland were significant negatively associated with food shortage. Procurement of food on credit from ration shops was found to be a predominant strategies to cope with food shortage, followed by borrowing food from neighbours and relatives. Conclusion In nutshell, the study shows that households from non-mines affected villages were at high risk of food shortage. However, percentage expenditure on food indicator reveals that household from mines affected villages was comparatively more vulnerable to food shortage than its counterpart. The membership of any socio-political organization emerges as a main factor which reduces the risk of food shortage.

The role of migration and remittances sent by the migrants is a matter of debate in the existing literature on migration research. Using the nationally representative data from the 64th round of National Sample Survey, this paper contributes to the debate about the impact of internal and international remittances on poverty reduction in Uttar Pradesh and Bihar. In the list of states in India, these two states are often placed at the top, for their high out-migration rates and low progress in social and economic indicators. This paper begins with a discussion of migration, remittances and poverty at the household level. A huge diversity exists in the utilisation of internal and international remittances in the areas of origin. The estimate reveals that internal and international remittances not only reshape the life chances of remittances receiving households but also fulfil the diverse non-food necessities. The result from the multivariate logistic analysis shows that households from rural areas received higher remittances compared to urban area. Thus, it gives strength to absorb the risks and shocks of catastrophic health, marriage expenditure and incidence of crop failures to the rural households. In line with an optimistic view, the findings of the present study show that remittances based migration enhances the socio-economic status and reduces poverty of migrant households. Based on propensity score matching technique, the results also show that the impact of international remittances on reducing household poverty out-weigh that of the internal remittances in Uttar Pradesh, but in Bihar, domestic remittances play a significant role in reducing poverty at the household level than international remittances.

For the countries of the Hindu Kush Himalaya (HKH) region, the importance of migration continues to be significant for livelihoods. Migration governance, therefore, is a critical priority (well-established). This chapter focuses on labour migration in the eight HKH countries. It explores the countries’ overall migration experience and, where possible, highlights findings specific to mountain areas of the HKH.

Some scholars of Indian history believe that Hindu–Muslims riots were a rare occurrence before the late 19th century; however, others have contested this. The country saw a new low in Hindu–Muslim relationships at the time of two major political issues — the Shah Bano case during the 1980s and the Babri Masjid–Ram Janmabhoomi dispute during the 1990s — that divided people from both communities and led to communal agitations. This chapter examines Hindu–Muslim riots and presents a systematic analysis of the spatial pattern of riots and its demographic correlates in urban areas. The demographic anxiety among Muslims of being overpowered by Hindus who were not only in a majority numerically in British India but also better educated than Muslims, was the most potent factor for the demand of the creation of Pakistan during the freedom struggle.

This chapter highlights that India is one of the most vulnerable countries to climate change as India has a large area in highly vulnerable regions such as coastal zones, mountains and dry lands, and vulnerability in these regions was compounded by underdevelopment and a large population dependent on rain-fed agriculture. It also presents a theoretical framework that underpinned on identifying overlapping hotspots for migration and global environmental change. The concept of vulnerability is central to the theoretical framework. The concept of vulnerability is defined as the likelihood that an individual or group exposed to the adverse impact of climate change and their capacity to adjust to it. The theoretical framework consisted of a series of variables – exposure to climate change; the underlying socioeconomic conditions; external drivers such as globalization, political factors and conflicts – that either singularly or in combination influences the vulnerability of communities leading to mobility outcomes as a livelihood strategy. The framework views vulnerability as the net outcome of interaction between climate change stress and the socio-economic capacity to adapt. Migration is one of the potential means of adaption to climate change. The study examines the pattern of migration in relation to the exposure of Indian agriculture to the impacts of climate change and globalization. On the other hand, coastal states are more urbanized and some of them are net inmigrating states. It is estimated that a population of about 73 million live in the low elevation coastal zone (the area located between 0 and 10 metres above sea level) comprising about 3 per cent of the land area and 6 per cent of India’s population. The study demonstrated that high inmigration and high biophysical vulnerability overlap in the case of coastal regions. In dry land regions that are characterized by high biophysical vulnerability, the matrix indicated that there is very high outmigration as well. Thus, it is essential to take into account the migration outcome of climate change, its role in promoting adaption and resilience in the areas of origin.

Census is considered to be a scientific exercise. However, it leaves a deep impact on religious and ethnic identities. This is because through census enumeration not only are boundaries of communities fixed, but also actual size and growth are known. This adds a new sense to the identities of the religious communities in the sphere of democratic politics. In India, the census was started around 1872 during the British rule, seven decades after the first census was held in Great Britain in 1801. The question on religion was included right from the first Indian census, unlike the British census which only included it in 2001. This paper shows that the inclusion of the question on religion, and the consequent publication of data on size and growth of population by religion during British rule, invoked sharp communal reactions. The demographic issues found a core place in the communal discourse that continued in independent India. The paper argues that the demographic data on religion was one of the important...

Temporary labour migration has rarely been studied at macro level despite its high prevalence in India. Drawing from the recently available Indian National Sample Survey (2007–08), this paper aims to study the basic differentials between temporary and permanent labour migration at the national level and examines the socioeconomic determinants of temporary labour migration at the state level. The study shows that temporary migration is seven times larger than permanent migration, and is largely a rural phenomenon dominated by rural to urban migration. A regional pattern in temporary labour migration is evident in the low-income Central and North Indian states. Low economic, educational and social status significantly induces temporary labour migration in contrast to permanent labour migration. As such, temporary labour migration appears to be a survival strategy of the rural poor in India.

In recent years, there has been a change in the thinking of policymakers about urbanization in India. In the Eleventh Five-year Plan (2007-2012) it is argued that urbanization should be seen as a positive factor in overall development, as the urban sector contributes about 65 per cent of GDP. There is also a growing realization that an ambitious goal of 9-10 per cent growth in GDP depends fundamentally upon a vibrant urban sector. As India is implementing the Twelfth Five-year Plan (2012-2017), the urban transition is considered to be one of the major challenges, requiring a massive expansion in urban infrastructure and services. Against this backdrop, the results of the 2011 census assume enormous significance in enhancing understanding of the magnitude, growth and interstate variations in the levels and rate of urbanization. Urbanization has increased faster than had been expected according to the 2011 census. This has reversed the declining rate of urbanization witnessed during the 1980s and 1990s. Also, for the first time since independence, the absolute increase in the urban population was higher than that in the rural population. In this article an attempt has been made to study the trends, patterns and components of urban population growth in the light of the results of the 2011 census.

This study is an attempt to explore the perception of city dwellers on different aspects of urban environment in the city of Bhubaneswar in India, and analyze its socio-economic correlates. The survey carried out for the purpose and the composite indices computed afterwards indicated that migrants were less satisfied with the urban environment and services, in comparison to the natives. It was clearly evident that there existed a wide disparity in service provision to slum and non-slum households. As regard the road transport service, the least satisfied were the affluent residents of the good residential area Interestingly, the respondents did not think lack of public transportation facility as a major problem, which could be attributed to the increasing tendency of using personal vehicles by them. It was also marked that with increasing age of the respondents, level of satisfaction with urban environment came down. Older people, who had been exposed to better environment earlier, were relatively unhappy with its current state. DOI: http://dx.doi.org/10.4038/besl.v11i1.3071 Built - Environment - Sri Lanka, Vol. 11 , Issue 01 : 2012: 7-13

As India has embarked upon economic reforms during the 1990s, published data from the 2001 Census provides an opportunity to study the country's urbanization process with reference to regional inequality and to the contribution of the components of urban growth, namely, natural increase, emergence of new towns, and the net contribution of rural to urban migration. India has more than 4000 cities and towns, which comprise 28 per cent of India's population of 1028 million as enumerated in 2001. However, about two-fifths of India's urban population live in only 35 metropolitan cities. The rate of urban population growth slowed down during the 1990s despite the increased rate of rural to urban migration due to a significant decline in natural increase in urban areas. This has led to an observable slowdown in the pace of India's urbanization.

The lack of data presents a fundamental challenge in measuring internal or international migration. Focusing on the case of India, this research note tackles the following aspects in the measurement of internal migration in India: a survey of migration-related questions included in various censuses, an assessment of the different criteria to determine migration status, and a comparison of migration data derived from census data and the National Sample Survey. Due to recent developments, there is a need to review these approaches to ensure that they capture new realities.

Although internal migration in India has been shaped by urbanization, its actual contribution vis-a-vis components of natural increase and rural to urban classification remains low (about 20 % of urban growth). On the other hand, while inter-state migration has been an issue of political conflict, the fact remains that majority of the people move within the state boundaries. Another important finding from this study is that male migration has declined, while female migration has increased since the economic reforms initiated in 1991. The decline in male migration in rural areas is sharper than in urban areas. The possible reasons for the decline in male mobility are: insufficient job creation during the last two decades, a stagnation of job opportunities in the organized sector, rising commutation of workers, and the employment guarantee scheme initiated in rural areas. Increased female migration seems to be the result of increased marriage and family associated migration. This chapter throws light on the emerging pattern of internal migration in India.

There has been euphoria among the government circles recently to develop Mumbai as a world-class city before the 26/7 floods hit the city. The cities like Shanghai or Singapore were often cited as benchmarks for planning and development of Mumbai in the next decade. However, the dream has been shattered by the unprecedented flood of July 26. Lack of urban planning, unprecedented rains and the failure of the early warning system are some of the important factors for the tragedy. It is the time that Mumbai’s planning and developmental discourses can be unshackled from an illusion of Shanghai or Singapore.

This paper modifies the measurement of dependency and applies it to the Indian situation at the state level. It is generally believed that the aged are a burden on the family and the nation as they do not contribute to the national income. This is not always true. In India: 40 per cent of those aged 60 and over are working, which rises to 61 per cent in the case of males. On the other hand, there are adults (age group 15–59) who are not working and are dependants. In the measurement of dependency, adjustments for these factors are essential. This study employs three measures of dependency, namely (i) old age economic dependency, (ii) adult dependency and (iii) relative dependency. Based on these dependency ratios, inter-state variations and gender differentials in dependencies have been studied. The study shows that relative dependency of the old age population is lower than the adult population, and the opportunity of harvesting the demographic window is being missed in India.

Rural-urban classification constitutes an important framework for the collection and compilation of population data in many countries. While “urban” is often specifically defined, “rural” is treated simply as a residual category. The criteria defining urban also differ from country to country. This paper argues that these rural and urban statistical categories are also highly significant for local governance, increasingly so in recent years given the emphasis on local governance and its restructuring. In India, constitutional amendments have given constitutional status to local bodies in the federal structure of the country. Local bodies are thus now expected to draw up their own plans and initiate development works, which requires them to generate their own resources and lessen their dependence on central government funding. It is thus necessary to reorganize urban space into viable spatial units in terms of their revenue base. While rural-urban classification is the task of the Census of India, state governments are responsible for granting municipal status to urban centres. This paper examines the criteria and limitations of the rural-urban classification followed by the Census, its congruence with the dynamics of state-accorded municipal/non-municipal status and some implications for municipal governance in India.

In a developing country like India metropolitan cities act as a pole where development takes place first, get concentrated and spread to the other geographical regions. As city grows and gets mature this process of development and its internal structure also changes simultaneously. After a certain stage of development, the population of metro cities starts shifting outwards and urbanization spreads over the adjoining areas. In this situation, the population growth either is stagnant or even declines in the core areas of the urban agglomeration. Kolkata city is one such example. Kolkata became the first million city of India in 1901 and experienced fast growth until 1971; afterwards growth rate plunged down. As per the census 2011, the decadal growth rate of the Kolkata UA was just 6.87 %, well below the natural growth rate of West Bengal and India.

Reactive infiltration is a fast and cost-effective technique for manufacturing ceramic-matrix composites (CMCs). CMCs are used in elevated temperature applications like rocket engine casings, jet nozzles, gas turbine blades and nuclear cladding. There is an urgent need for minimizing experimental costs as well as optimizing process parameters during manufacture, so that we have minimized manufacturing costs and reduced infiltration times. Towards this end, the objective of this research was to develop an integrated micro-macro model of reactive flow of molten silicon in a porous preform consisting of carbon-coated silicon carbide fibers and then optimize process parameters computationally. The overall objective of the research was to arrive at a modified equation of Darcy's law for flow through a porous medium with the help of numerical/computational modeling. This paper deals with the flow of silicon through porous carbon at the macro level. The macro flow of silicon was integrated with an available micro model by determining the transient porosity from the micro model and using it in Darcy's law written for the macro flow of silicon. From the results of this study, we recommend suitable process parameters such as initial temperature of the solid reactant and the specific kind of reactants to be used for achieving complete infiltration. These conclusions are drawn after observation of the rate of decrease of permeability with more reaction.

Relatively low fracture toughness of WC-Co materials compared to high speed tool steels is a major concern. Tungsten carbide tools may exhibit sudden brittle fracture at high stresses such as are encountered in shear and slitter knives. This has limited the use of tungsten carbide tools to certain applications in spite of their high hardness and wear resistance. The objective of this investigation is to evaluate the tribological performance of selected cermets and develop a fracture mechanics wear model. Six compositions of WC-Co materials (Co ranging from 4 to 30% by weight) with or without TiC, NbC, TaC, or Mo2C were selected for relating wear modes of these tool materials to pertinent mechanical properties such as fracture toughness and hardness. The influence of mechanical properties such as Young's modulus, hardness, fracture toughness, modulus of rupture, and Weibull modulus on wear rates and wear modes of the selected materials is presented and discussed. The major mechanisms of wear in WC-Co materials are discussed as they apply to the development of suitable relationships between wear and mechanical properties. The wear process is by the transfer of steel from the ring to the cemented carbide block specimens, initiation of mode I cracks normal to the mating surface, propagating of mode II cracks parallel to the wear surfaces and the subsequent separation of platelets with adhered WC and Co particles through adhesive forces with the steel ring. The wear rates of the cermets do not show a consistent relationship with mode I or mode II fracture toughness, but a general trend of decreasing wear rate with hardness is seen. This suggests that the tribological performance of these cermets depends on certain specific functions of pertinent parameters including fracture toughness, hardness, applied load, coefficient of friction and microstructural characteristics. A fracture mechanics-based wear model has been developed to relate the steady state wear rate (W52) to hardness, mode II fracture toughness, coefficient of friction, and applied load.

Discontinuously reinforced aluminum alloys are viewed as candidate materials for elevated temperature applications because of their attractive high temperature strength properties and wear resistance. The elevated temperature elastic properties and the failure characteristics in relation to the preform flaws, however, have not received much attention in spite of their potential significance. These issues are studied for an aluminum-silicon alloy reinforced with mullite discontinuous fibers, fabricated using the squeeze infiltration technique. The effect of preform flaws (shot) on room temperature strength and ductility is investigated for composites seeded with different amounts of shot. The Young's modulus of the composite exceeds that of the unreinforced alloy over a wide range of temperatures, and the beneficial influence of the fibers is especially significant at elevated temperatures. The primary contribution to the reduction in the modulus of the composite at higher temperatures is shown to be the degradation in the matrix stiffness. Reinforcing the alloy with mullite fibers results in only a moderate improvement in strength at room temperature but the elongation to failure is reduced considerably. Increasing the amount of shot, although not appreciably degrading strength, further reduces the ductility. Shot is found to play an important role in the damage evolution by fracturing early in the loading process, and thus, the composite integrity when subjected to slow stable crack growth, as in fatigue, for example, could be adversely affected.

Aluminum matrix composites with reinforcement of planar-random graphite fibers, SiC whiskers, or alumina particulates have been evaluated for their high temperature performance. The composites were aged at 150 and 200°C for up to 500 hours. Microhardness results indicate accelerated aging of the composites in comparison with that of wrought 6061 Al resolutionized and aged under identical conditions. The aging response of the composites depends on the characteristics of the reinforcements. The graphite fiber reinforced composites and the silicon carbide whisker reinforced compos ites retain their tensile strength and stiffness in the overaged condition of the matrix. The composites were tested for their tensile stiffness and strength at temperatures of 150 to 350°C. The Young's modulus of all the composites remain relatively constant up to 350°C. Both the graphite fiber and silicon carbide whisker reinforced composites show substantial strength advantage over that of the wrought 6061 Al at all temperatures. The silicon car bide whisker and alumina particulate composites were evaluated for their creep behavior. These composites were subjected to creep deformation at temperatures of 232 to 350°C under stresses of up to 100 MPa. The whisker reinforced composite shows significant re sistance to creep; about two orders of magnitude lower steady state creep rates than that of the wrought aluminum. The particulate composite had a moderate increase in creep resistance.

The aging characteristics, elevated-temperature strength and stiffness as well as creep deformation of aluminum alloy 6061 composites reinforced with silicon carbide (SiC) whiskers (Vf=0.20) have been studied. The peak hardness for this composite was 148 kgf mm−2 after aging for 18 h at 150 °C and 138 kgf mm−2 after aging for 1 h at 200 °C following solutionization for 15 min at 530 °C. The maximum tensile strength was retained after aging for 18–55 h at 150 °C, an improvement of 40% over that of wrought aluminum. The tensile strength of the received composite decreases from 578 MPa at room temperature to 229 MPa at 350 °C. In terms of the use temperature, the composite provides an advantage of approximately 200 °C over that of wrought aluminum. Young's modulus for the composite remains almost constant (104 GPa) from 150 to 350 °C, and it is 58% higher than that of the wrought aluminum at 150 °C. Experimentally determined values of the steady state creep rate range from 4.9 × 10−9 to 1.3 × 10−6 s−1 for the composite which shows substantial resistance to creep deformation with respect to the wrought aluminum alloy. The activation energy and stress exponent for the composite are reported and discussed.

An overview of the major casting-based manufacturing techniques of metal matrix composites is presented. These techniques include compocasting (rheocasting), squeeze casting, infiltration, investment casting and pressure casting (squeeze infiltration casting). This is followed by a detailed description of the high pressure infiltration casting (HiPIC) recently developed at the Applied Research Laboratory of the Pennsylvania State University. HiPIC uses a rapid application of a relatively high pressure (above 100 MPa) to force-infiltrate molten metal into fiber pre-forms. Reaction between fiber and matrix metal is negligible and the cast composites are free from voids, gas porosity and shrinkage cavities. Experimental results on tensile strength, stiffness, low cycle fatigue, fracture toughness, damping and corrosion resistance of the HiPIC composites are summarized and discussed.

The hardening rates of 6061/SiC/20w and 6061/Al2O2/15p are significantly higher than that of wrought 6061 Al. The whisker composite retains its tensile strength over a broad range of aging times (up to 500 hours). Under identical aging conditions, the tensile strength of the whisker composite is about 65% higher than that of the particulate composite and wrought aluminum. Likewise, the stiffness of the whisker composite is approximately 60% higher than that of the other two materials (which have similar stiffnesses). At 350°C, the whisker composite has about 55% higher strength than the particulate composite and the wrought aluminum, in comparison with a 111% advantage at room temperature. The whisker composite shows better resistance to creep than the particulate composite and wrought aluminum; the improvement is almost two orders of magnitude in terms of the steady-state creep rate.

Metal-matrix composites may offer better damping properties than unreinforced alloys. Because damping properties (and metal-matrix composites) are becoming important in airframe design, the damping capabilities of a number of aluminum-matrix composites were measured over a wide range of frequencies at low strain amplitudes, using a new laser vibrometer technique. Silicon carbide and alumina reinforcements resulted in a material with damping properties similar to that of unreinforced aluminum 6061-T6, but unidirectional and planar-random graphite continuous-fiber reinforcements increased the damping by 5 and 14 times, respectively. The increased damping of the continuous fiber composites is attributed to the absence of interfacial reaction resulting from the high-pressure infiltration method used for their manufacture.

In an emerging thermal spray process a coating is formed by exposing a metallic or dielectric substrate to a high-velocity jet of solid-phase particles, which have been accelerated by a supersonic gas jet at a temperature much lower than the melting or softening temperature of the particle material. This is known as "Cold Gas-Dynamic Spray" (CGDS) method. Using this method, 2618 Al substrates were coated with nickel-aluminum bronze powders (~100 and ~400 mesh) in an effort to obtain improved wear resistance. The coatings have been examined for their microstructure, hardness, and bond strength. Triple lug shear tests performed on coated panels provided quantitative measurement of the coating/substrate interfacial shear strength. The steady state wear rates were determined using the pin-on-rotating ring test at a pressure of 690 kPa and a sliding velocity of 9 m/s. The wear resistance of the nickel-aluminum bronze coatings is discussed in conjunction with scanning electron microscopy (SEM) examination of the wear tracks and metallography of the polished transverse cross-sections. Though the coatings are not completely free from porosity, they exhibit high interfacial shear strength and wear resistance due to the low-temperature, ballistic impingement of the powders in the cold gas-dynamic spray method. The ~400 mesh powder coating shows higher interfacial shear strength and wear resistance in comparison with the ~100 mesh powder coating.

Ceramic matrix composites (CMCs) are being considered for a broad range of aerospace applications that include various structural components for the aircraft engine and the space shuttle main engine. Use of silicon-based CMCs which have high thermal conductivity, allows for improvements in fuel efficiency due to increased engine temperatures and pressures, which in turn generate more power and thrust. Furthermore, CMCs offer significant potential for raising the thrust-to-weight of gas turbine engines by tailoring directions of high specific reliability using design-based fiber architecture. One of the low-cost processing techniques for the silicon-based CMCs is the reactive melt infiltration [1] of silicon into the preform of carbon-coated silicon carbide fiber. However, fabrication of high performance SiC/SiC composites requires a deeper understanding of the infiltration kinetics such that fibers are protected from adverse reaction with the molten metal, that the preform is thoroughly infiltrated, and that there is no residual silicon left unreacted.

Several graphite fiber reinforced (planar random) metal matrix composites employing copper, aluminum, tin and babbitt matrices were fabricated by a newly devel oped high-pressure squeeze casting method. The fiber volume fraction of these composites ranged from 5 to 55%. These composites had relatively weak fiber-to-matrix bonding because of the near-absence of interfacial reaction between fiber and matrix materials. The tensile strength of these composites increased with fiber volume fraction up to about 25% followed by a gradual decrease for higher fiber volume fractions. Experiments were designed to evaluate various mechanical and physical properties of high pressure squeeze cast composites including the damping capacity and corrosion re sistance. Measurements of logarithmic decrement values at reasonant frequencies on can tilevered beam specimens have demonstrated that the damping capacity of the composites is much superior to that of wrought 6061-T6 Al and mechanically alloyed aluminum. Results on corrosion resistance of the composites in distilled water and 3.5% NaCl solu tion over a range of voltages and temperatures are presented and discussed.