Are there any significant differences between words trip, travel, and journey (nouns)?
Are those interchangeable words or are there any specific expressions which uses one of them but not another?
These three words can be synonyms, but have slightly different connotations.
First, travel is usually a verb...
I will travel to Washington DC.
...but not always. In common speech (at least as far as I am familiar), when used as a noun, it is used in its plural form:
How were your travels?
Compared to the substantially equivalent sentences:
How was your trip?
How was your journey?
One could also ask How was your travel?, but it this would have a more specific meaning, for instance, "How was your flight from New York to L.A.?" as opposed to "How was your entire journey, and the time you spent in L.A.?"
Trip and journey are more closely interchangeable, and vary mostly in duration, distance, and formality.
A trip can be a short journey. One can take a trip to the store, but it would be unusual (except in poetic exaggeration) to take a journey to the store
A journey would often imply a longer (in terms of time and/or distance) trip, perhaps to multiple destinations, or with a greater sense of unknown. A journey may not be fully planned out ahead of time.
A business conference to Seattle would probably be described as a trip, whereas a family vacation road-trip from Nebraska, through the Colorado Rockies, camping in Nevada, then stopping in Las Vegas and returning through Oklahoma and Kansas, might be described as a journey.
Often, in colloquial English (at least in the U.S.), trip is far more commonly used than journey, even when describing long/epic travels.
Both trip and journey can also be verbs, but when used as verbs they are not interchangeable. To journey is to engage in the act of journeying:
We journeyed to the Grand Canyon.
However to trip is to cause someone to stumble or lose their balance.
She tripped the thief with her cane.
I tripped over the dog.
To trip up has the additional connotation of causing someone to blunder:
The reporter tripped up the senator.
There are also some additional cases where trip and journey cannot be interchanged in some common expressions:
Are there any significant differences...?
Yes, there are. The context defines. I would suggest the following rule of thumb:
Travel by air nowadays is cheaper than before.
If your time permits, take a boat trip to the Samui island.
After receiving an annual bonus, I went on a trip to Thailand.
I'm often away from the office on business trips.
Did you have a good journey?
On my journey to work, I listen for music;
I went on a tour of France.
His voyage around the world took three years.
A voyage through space.
There are small differences between these words. For one, travel is more commonly used as a verb than a noun. You won't really hear someone say "I'm going on a travel", but you'll often hear people say "I'm going on a trip"
As for trip and journey, trip usually refers to a small casual outing that can be anywhere from a few days to a few weeks. Journey, however, has a more epic and grandiose connotation associated with it. These may span several months and thousands of miles. Historically, journeys occurred more often when there weren't modern forms of travel and one had to walk from one side of the continent to another.
Take for example "Journey to the West", a popular work in Asian cultures about traveling to another continent to obtain the scriptures. This journey was long and epic, and had multiple adventures within in. As such, journey is less used in modern day, but you may see it more in works of fiction.