Can a Muslim woman travel and study overseas without a mahram?
Like to pursue her masters or on university exchange. Can her husband prevent her from going if he isn't comfortable with her going?
There is rule of thumb in Islam that a Muslim woman must be accompanied by mahram, when she has to go out of her home for a longer term, be it for travel, education, or anything. So permission of husband or any mahram does not matter, when our prophet Muhammad himself prohibited it.
Here are ahadith about it:
Ibn `Abbas (May Allah be pleased with them) reported that the Prophet (PBUH) said, "No man must not be alone with a woman except in the presence of her (Mahram). No woman should travel except in company of a (Mahram).' A man said: "O Messenger of Allah! I have been enrolled for such and such expedition, and my wife left for Hajj.' He (PBUH) said to him, "Go and perform Hajj with your wife." (Al-Bukhari and Muslim.)
Al-Bukhari and Muslim narrated from Ibn Abbas -may Allah be content with them- that Rasulallah (saw) said:
«لا تسافر المرأة إلا مع ذي محرم» “A woman should not travel without a Mahram”.
Sayyiduna Abu Saaid al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (may Allah bless him & give him peace) said: "Let no woman travel for more than three days unless her husband or a Mahram is with her". (Sahih Muslim).
Sayyiduna Abu Huraira (may Allah be pleased with him) narrates that the Messenger of Allah (Allah bless him & give him peace) said: "It is unlawful for a woman who believes in Allah and the last day that she travels the distance of one day and one night without a Mahram accompanying her". (Sahih al-Bukhari, no. 1038).
I hope no doubt is left after these ahadith.